Thanks for that post, Damon. You have some good details and information that I was missing.
I first learned that it was possible to use 944 rear suspension on a Bug from an article in a book I found a Carlisle a few years ago. (I remember being incredibly surprised that Porsche was still using essentially the exact same suspension geometry as VW had been using for more than a decade. Must have been a good design!)
I never got around to doing the installation on my car...yet...but I did go as far as to pick up a pair of complete 944 trailing arms with hubs, brakes, etc.
Below are some old photos from my archive that I took the weekend the trailing arms were delivered. You can see how similar they are to the Bug trailing arms. And you can also see the differences: The brake rotor are MASSIVE compared to the Bug's, and the whole arm is much beefier and stronger.
I've been told that you have to alter at least one of the bolt points where the spring arm attaches, and you have to machine the urethane donut where the arm attaches, both of which are relatively minor modifications. It still blows my mind that these two cars -- a little beetle-shaped passenger car from the '60s and '70s versus a front engine, rear drive sports car from the '80s -- can share these parts. Pretty cool.
I didn't know that it increased the track a little. Thanks for that information.
For those of you who don't already know, an inch = 25.4 mm. So according to Damon's info, the conversion ads about an inch to the track, overall. (Or three inches in the later models of 944s).
Here are the photos of 944 turbo trailing arms sitting next to the stock Bug trailing arms on my blue Sterling: