Use a cable for a C4 auto vintage mustang. You'll need the T5 backup light connector to connect it into the backup light wiring, but you could get by with spade tips instead. I have no idea why there would be mixed reviews on the swap, or why it would be considered all that hard. With all the right conversion stuff, it bolts right in, that can't be hard!
Enlarging the shifter hole is usually for installing the shifter with the
trans installed. If you install the shifter and then put the
trans in, then install the stick with it in, you won't have to cut. That's the way I'm doing mine, I'd like to be able to get mine close to stock if I ever wanted, so hacking is bad on my list.
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66 coupe 5.0/T5, home-brewed power 4 wheel disc setup, 350hp+, looks like it belongs in 1968