AT Power in the UK have DBW throttle-bodies in sizes up to 80mm diameter which might suit this project .....
I have been intending to use 50mm ITB based on the Jenvey kit (which looks a lot like where the GTM kit in the 1slow370 thread came from), but I am now re-thinking my options.
Look here:
Fly-by-Wire Throttle Bodies, AT Power Online Shop
The Unitech 350Z DE engine used a fabricated manifold and a single 90mm TB to achieve ~500hp @ 9000rpm on the Fontana Racing Z33 that is now in Canada (and it now has a HR heads on a HR block with JWT pistons, rods, C11 cams and ITB if my reading of Sasha's posts is correct).
Hmmm .. lots of options..