The bike is a late 70's CB750 and the tank is an aftermarket aluminium number designed for the SR400. We cut the bottom out of it and fitted a new tunnel, and moved the fuel tap over to the left hand side.
It's now gravity fed rather than vacuum. Slots in quite nicely.
And this is my favorite bit - we fabbed up some new mounts on the tank so it can bolt down to the bike firmly - the tabs allow the seat, which is also an aftermarket item, to lock surely in place.