Best conversion I ever saw in a Z-car wasn't a V8...
I was talking to this bloke about gearboxes and he mentioned some issues he had fitting a Supra box to his son's 260Z. It never dawned on me then, but there's no earthly reason to fit a Supra box to a Z-car, they already have a fairly good 5-speed.
Then, when it did come to me, I asked the inevitable... "Why did you fit that?"
"It was a better fit for the Hemi 6 engine we put in," came the reply.
Seems the Hemi, though a bit longer than the original OHC engine, is a little lighter. And being substantially larger (1.5 litres or so), it produces plenty of power. The only body change required was that they needed to make the striker mount for the hood latch removable, which wasn't so hard.
It has a 4bbl and a mild cam, probably good for about 230 or 240hp, almost a hundred up on standard with gobs of torque.