I read on here somewhere that certain vintage VW will fit our 1200s?

if it's true would this setup work?

Complete kit for any IRS bug 4 lug rear discs with rotors, calipers, brackets and hardware install... (Volkswagen VW Bug Type 1 rear disc kit )

how does that work since our cars are not IRS, but 510's are.

I've been working on the rear disks problem and the shop i've been working with tells me they have rear disk brakes for a 210. They use wilwood calipers a little plate that goes where the backing plate for the drums went, or something like that.

how do the VW brakes mount? I'd still use the wilwood calipers brakes and VW are somewhat dubious, as well as the pad composition is probably only 1 or 2 types.

What about if I dont hook up the IRS from the BUg? would it still work granted all hardware measurements fit?

Possibly, but I haven't heard anything like this before. There are reports that certain VW shocks or struts fit (i think it was golf (rabbit) struts maybe?).