The old setup had to go because it consisted of a tall geared bug tranny (3.88 and big tires with a gutless engine = no no) and the engine was a1600 dual port but had a 1500 single port carb adapted to it. It ran out of breath by 4k and had an annoying flat spot just off idle. It only had power between 2k and 3k. Above or below was gutless.
I picked up a 3 rib bus tranny 002 model from a '77 or so. It has the extra mounting ears on top of the bellhousing if you know what I'm talking about. It should have a much better 5.37 or something ratio.
and a mounting kit
a KEP adaptor
and flywheel (used, obviously)