First, let's get familiar with the two different guibos on the market that fit the XR4Ti and Scorpio driveshafts. The guibo on the left is new BMW guibo. This guibo is the same as the guibo that came in both Merkurs originally. It has a cross section that has a somewhat square profile and has no tabs on the metal sleeves. The guibo on the right is a new Fiat part. This one has a cross section that is round and has six metal tabs on it, three on each side, at alternating metal sleeves.

Both guibos have an identical bolt circle.

We'll get to the metal tabs in a little bit and discuss why they don't allow the guibo to fit properly in this application. If you've got a Fiat guibo, my first suggestion is to get the BMW part, but if that doesn't make sense for you, prepare to remove the tabs. That's discussed in detail later on. In the meanwhile, let's talk about the installation of the guibo.
The steel band that is installed around a new guibo is there to control the diameter of the bolt circle in an attempt to make installation easier. The guibo is made almost completely of rubber bonded to a few steel sleeves. The steel band is under tension so the rubber is compressed. This is what should keep the bolt circle at the correct diameter. In practice, this band should remain installed until all six bolts holding the transmission yoke and the driveshaft to the guibo are torqued.

What we've found during every single guibo installation is that this band holds the bolt circle to a diameter that is close to correct but not quite. This means every guibo is a fight to install.

It doesn't have to be this way!
The solution to this problem is very simple. The first step is to remove the steel band.

I used a pair of pliers to remove the tab at the end of the steel band. Use caution with this step as the steel band is under tension and it pops free with a little bit of force.
Next, select a worm drive hose clamp that is large enough in diameter to fit around the outside of the guibo. Clamps like this are inexpensive and it's essentially a tool you'll have around for the next time a guibo needs to be replaced in your fleet of Merkurs.
Install the clamp around the outside diameter of the guibo. We prefer to use a small socket wrench to do the tightening. A socket wrench is much faster than a screwdriver. There's no reason to crank it down yet. Just get it on there so it doesn't come free.
We're going to take a brief pause right now to talk about the proper way to torque a bolt and nut assembly. (A bolt, incidentally, is typically defined as a threaded fastener that passes through an unthreaded object and is tightened down by nut on the other end. So, if you're threading a bolt into something, like a driveshaft-to-differential flange connection or a cylinder head bolt into a engine block, that's technically a machine screw.)

Whenever you are applying torque to a bolt and nut assembly, you should always apply the torque to the nut. The bolt head should be held stationary. The purpose of this is to ensure that the torque that the torque wrench is measuring is just the friction of the deforming threads of the nut and the bolt and the friction between the nut and whatever surface it is tightening down onto.

If you are turning the bolt, then you add the extra friction of the bolt shank turning inside whatever the bolt is passing through. This extra friction means you get less clamp load for the specific torque value. There are no positive benefits from this.

So, when you are ready to tighten the bolts, do it like the picture shows; hold the bolt head with a wrench and turn the nut with the torque wrench.
If you have a Fiat guibo with the metal tabs, now is the time to really start paying attention.

We're ready to try fitting the guibo to the driveshaft and transmission yoke. Of course the first bolt slides in without a problem.

You'll note that in the picture I have the tabs on the guibo resting against the mounting ears on the driveshaft. Essentially, the tabs are pointing toward the bolt heads. If they were in the opposite orientation - with the tabs pointing toward the nuts, you'd discover that you can't put anything on the nut except an open end wrench. This is why I mentioned the correct method of applying torque in my previous post. Because of this fact, the tabs, if left on the guibo, must be oriented as shown - tabs pointing toward the bolt heads.

Unfortunately, the tabs interfere with the mounting ears on the driveshaft, which mean that no amount of adjustment of the clamp tool around the guibo will allow the bolts to pass through the guibo. In fact, this picture shows exactly how much we were able to install the bolts into the guibo before everything got completely bound up.
Just as a demonstration, if you index the guibo so the tabs aren't on the mounting ears, the bolts slide in beautifully.
The clamp tool allows the bolts to slide in effortlessly after you use it to adjust the guibo's bolt circle to the right diameter.

Now we don't have a choice but to remove the tabs from the Fiat guibo. Again, if you have a Fiat guibo, I recommend you simply replace it with a new BMW unit.
The main problem with grinding the tabs off is heat. Remember that you have steel sleeves which are bonded into solid rubber. If you get too much heat into the rubber it could shorten the life of the guibo dramatically. This is the primary reason why we recommend the BMW guibo. (The BMW guibo also has a more substantial cross section which we assume makes it stronger, but we don't know that for a fact.)

When we did this installation, we clamped the guibo in a vise and used an angle grinder to carefully remove the tabs. We'd stop frequenty to keep the metal cool. All in all, the modification tool about 30 minutes.
After the tabs were removed, begin installing bolts and adjust the clamp tool to fine tune the bolt circle diameter. It's easy to get this correct and even easier to complete the job.

The torque specification for the nut is 66 lb-ft.
Here's one final note before you install the driveshaft in the car (which really should be mentioned at the start of this tech article, since the work needs to be done before the guibo is installed). There is a bearing in the transmission yoke that connects to a hardened boss on the front of the driveshaft. While you have the driveshaft out, please clean and grease this bearing before reassembly. Now is a great time to replace your center support bearing too.