It is a different engine harness. Ive done a few 6cyl to V8 swaps in HQs years ago, (mostly utes & tonners) & as far as I can remember the wires to the alternator & temp sender had to have a bit extra added to them. Im sure it wasn't a big job, but back then it wasn't a resto job, just to put the V8 in, so didn't worry about originality. It was the sort of thing you went home after work on a Friday in a 6 & by Saturday nite or sunday morning you would be driving a V8 4speed (with no exhaust) & all done with a trolley jack & endless chain & lots of beer.... so the wiring wasn't much of a problem

cheers
Max