First of all... this is one a brilliant looking project!

And about that Zetec conversion Iīd prefer the Blacktop for RWD installation, itīs some times easier to find than older Silvertop, and I quess itīs better for your plans for naturally aspirated use, mechanic valve lifters etc.

You propably know the main issues are oil sump and new position for thermostat, and of course engine mounts. You`ll find these all for bolt-on stuff from Retroford for example, but they are quite easy to fabricate by yourself too! Or thatīs how I did...

I made my oil sump out of 2mm sheet of metal, another way is to use Silvertop sump, but it needs TIG cause itīs aluminium.

Side mounts for Sierra installation I welded out of 6mm plate of steel, think even 3mm is fine.

I made my Zetec-RWD-conversion in last summer, and there is lots of pics in my project topic about water rail, sump and those side mounts, for inspiring at least..