My VS came with front discs brakes and rear drums. I replaced the rear drums with disc brakes were plug and play with no issues about "offset" or anything else. I started with the CB Performance rears and had the common problem of the separation of the hub's aluminum part from the steel part and replaced the hubs that were on the CB Perf. set up with the solid steel hubs from Socal imports. Hell yes, they are heavy but my Type IV engine can't tell the difference. Now my 4 wheel disc brakes are working perfectly and I have confidence that they will continue to do so. I would never have a Speedster without 4 wheel disc brakes and for sure, a high powered Speedster. Drum brakes are just one step better than the mechanical brakes I once had on a '34 Ford. We need all the safety we can muster on these plastic egg shell cars and I'd start with brakes that are reliable. This comes from experience with a very scary panic stop with rear drums on an interstate.
If I had it to do over I'd go with the Socal product to start with. Good price and it fits a pan based Speedster.