The A518 takes quite a bit of tunnel and crossmember work, and was never available with the big block bolt pattern, although adapters are available. This thread
42RH / A-500 in a Duster with pictures. will give you some idea of the fitment issues- although for an A500, the overdrive housings are the same with the same clearance considerations.
The SSA41 kit also makes no mention of a big block bellhousing being available. It also requires a computer and it's engine sensors (TPS, etc.) for shifting. They claim "no tunnel mods necessary", but don't mention crossmember mods. The trans is modified to accept a speedometer cable, which they supply.
The 200R4 supposedly fits with next to no mods, but any installs I have heard of were on smallblocks- so again you're on your own finding a big block conversion bellhousing. And getting a custom speedo cable.
@jbc426 runs one, maybe he can chime in on fitment.
