The weight issue always seems to be a large focus, even though a fully dressed aluminum LS is 440lbs. Trash the cast manifolds, ac compressor, emissions stuff, etc...and you have an engine that weighs what a KA weighs. Additionally, the LS and Ford 302 are ridiculously compact, being v8's. The LS is something like 25.5" long.
I'm a huge fan of these cars, and the purist SR/KA "keep it Nissan" theme. Power per dollar, depending on your skill set, its hard to beat the v8 power.
I've been curious about where a set of LS to S13 mounts would place the engine, when used in a 510.