I'd already had a measure up with the gearboxes side by side, and had decided that the shifter was going to be in something like the right place, so went about getting it bolted up to the engine, all went fairly smoothly aside from the top two bellhousing bolts being a complete twat to get to under the tunnel.
Turns out that it's a great fit, kinda wish I'd taken this route in the first place, instead of messing around with adapter plates etc. The shifter is dead centre, so will just need a little straight lever making for it, but I'll leave this as a last job once I've levelled up the engine and box.
Thats about where it all stands now, I've been playing around with both propshafts, and it looks like the rx8 one will work if I have the splined end from the old Ford shaft fitted, and a small spacer made up to go between the diff and the back end of the prop.