My guess would be FET, but I don't know for sure. Looks a bit long for a Mikuni manifold, plus this one has separate flanges and a central connector which I don't see on the Mikuni.
Measure the length and see if you can match it up: Triple carb intake length
EDIT: Whoops, definitely not FET. However, I'm almost certain that it is a Nissan Comp piece, Ã la BRE 240Z.