@Todd M- I forgot to add that irs trailing arms can be narrowed (I've heard of as much as 1 1/4" per side and not having to narrow the torsion housing), but it is a little involved, and then you have to come up with shorter axles (type 3 automatic left side is approx 1" shorter than beetle sedan irs axles and works). The point is if you want it bad enough, whether your car is swingaxle or irs you can put somewhat wider tires on the back of a classic Speedster bodied car.
Hi there, new to this forum and learning about Speedsters and Spyders.
I am not new to VW's though. I have narrowed an IRS rear on a 1958 LowLight Ghia. I used the Bruce Tweddle method, and moved the bearing carrier in 1 5/8" each side. I fitted a 205/65r15 under the fender, which is very tight on a Ghia. As left side type 3 automatic axles are hard to find, I bought Bus into Bug conversion axles, which are a little shorter than a standard bug axle. These axles do not have an inner shoulder like a stock axle, and they have a lot more spline. I than machined off some of the outer spline on both sides to the proper length and then cut new circlip grooves.