Not sure myself but with a 5k, you'll need a K50, peddle box, tail shaft depending on the splines, diff is the same, i'm pretty sure their cable clutch so no master cylinder and maybe a cross member. Dash cluster is the same. I think everything on a 4k can be bolted onto a 5k, just the carby will need re-jetting. I'd do the whole lot at the same time, cause i did the G.box in my car and now i want to put a 5k in but can't be stuffed. Other people will ellaborate and correct me.