After having successfully installed 5 of these on Zodiaco groups, I have a couple of lessons learned which I shall incorporate into the original post:

First off: using a cafelat silicone gasket is not required but is easier to form and makes the installation go a lot easier. Both the 8mm or the 8.5 mm gaskets will work, depending on the height of your preferred portafilter above the wings, but in general the 8.5mm gasket is more forgiving.

If your shower screen falls out after pulling a couple shots, it is most likely because the gasket isn't far enough up into the group. You can fix this either by stretching the dispersion screen a little more in the vice or by using a thicker group gasket and modifying the inner upper edge so the dispersion screen sits a little lower in the gasket.

Heh, I could, but it would be hard to make any machine specific adjustments oversees.

I'd have to make it fit mine and then just assume our groups were made the same

After making another one I figured I would take a quick snapshot about how the dispersion screen should sit in the gasket for a good fit, as its much easier to see than describe:


And just for fun, here are some modified shower screens and gaskets: my two groups, one I just finished making for another machine, and the original prototype with a generic E61 screen and rubber gasket:

Just did this mod on my faema velox and it worked awesome!! Just as easy if not easier than it sounds, took me maybe 30 mins total.

Hey dominico, do you have any issues with head space?? Mine almost seems like it could go a mil higher but I'd have to trim the top of the shower screen

I've noticed a slight difference in headspace in both of my groups, about 1mm actually. It seems that manufacturing tolerances in these groups were a little loose. I considered grinding the lip off the screen for one of them, but I didn't think it would make much difference to my shots, then again I don't usually overfill my baskets.

I was thinking of grinding a mil or 2 off the top of the basket. I'll leave it for now and see how the shots come

For the sake of completedness for this thread, member EspressoPhD came up with yet another way to seat an E61 shower screen onto one of these groups:
Faema Lambro

Thank you for this thread and for sharing the information.
Last week I finally made this modification also on my President. Work very good and it, after all, very easy to made.