I'm considering all sorts of options for my '65 220 with a B20. It currently has a partially locked up M40 (shifts between R, 1st and 2nd only) and I'd like to upgrade to a five or six speed. Considering an engine swap, as well, maybe to a B230f or similar. I know there are M46 overdrives available and have come across a few M47 five speeds. Any bolt ups or easily adapted transmissions I should be looking at? Any thing to stay away from?