hi guys newbie here I have a 1978 mk2 escort 1600 sport with a 1600 crossflow 4 speed box and a bourg warner rear axle. I was planning on getting the engine rebuild and tuned then bolt on a mazda rx8 gearbox which I already have the adapter plate for, but it's going to cost a grand and a half at least to get the engine running good and still not have a great deal of power and not be able to handle much with the rear axle. so then I thought what about more than just the gear box what if I got a donnar mazda rx8 and used all the running gear from that? plenty of power pick them up cheap as chips

Read this thread, pretty long, but stick it out. It may or may not persuade you either way.
https://www.locostbuilders.co.uk/viewthread.php?tid=181522&page=1