I remember years ago a guy put one into a Manta. It required a hood scoop to clear (tall engine). So with a GT, this will also require a scoop or bubble. Good engine though, they can routinely run 200K or more with little maintenance. And they can make pretty good power too, I got around 175 hp out of one I built for my cousin's pickup with dual Webers and a severely ported head, and I had a blower on my old Toyota pickup with a 22R (9 psi boost with 9.4:1 compression!).
I'd guess the weight is about the same as an Opel's, it has an aluminum head, but the crank, rods and flywheel are heavier than the Opel's.