Great info on your floor pan build. There is a VW house in western PA that sells bare to rolling reconditoned floor pans. It’s called Bugg Stuff. They have provided stock and shortened (Porsche Speedster) floorpans. They are always at the Import-Replica/Kit car nationals at Carlisle, PA in the Spring. I’ll try to post their phone & address. I may have their business card on file.
Only one year swing axle used a 12 volt system too, 1967. If you use earlier stuff, you’ll need 12 volt starter, coil, Alt/Gen, etc. Also the earlier year cars had single port heads. The newer stuff is all dual port.
As far as buying aftermarket, the earlier stuff, like wide-5 hubs, etc, are more expensive and not as available as the IRS/Dual port motor stuff. An IRS, 4 lug/dual port is the best way to go.
There is a company in New Zealand that manufactures an MGTF variant based on a Mazda Miata donor. It is all top shelf stuff. It comes as a “Pallet Car” like the Superperformance Cobra. It is built and strapped to a pallet less the Miata donor parts (drivetrain/suspension/etc.) It costs over $17K f.o.b. at the sole importer’s shop in, I think, Ohio.
Except for a TD kit that may be still made in Great Britain, that’s it.