[Orange97GTVert]

I don't know about the generator/alternator switch out, I don't know what all needs to be changed.

The 250 6 cyl engine didn't come out until 69, and I think the 3 speed had changed from the original, so I doubt the 3 speed is original. I have no idea which rear end you would have, I think the original with the 170 was a 3.00 :1, and in 69 I see it listed as 2.5:1.

My advice if you are serious about an engine swap is find an engine and transmission together from the same car, or better yet, find a donor car, because it would have the springs, wiring, engine, transmission, rear end, etc. Swap in the parts you need and then sell the donor car. Engine swaps are easy from V8 to V8, but there is a lot more involved in a 6 to 8 swap. Even the brake drums are different, all Mustangs 6's had 4 lug hubs.

Good luck!