I was just reading about the Muncie overdrive thing the other day. It didn't sound like a good idea. Give you the same first gear ratio as the M21 and it's quite a stretch to 2nd gear. Third is 1:1 and 4 th is like .89. Might be ok in the perfectly thought out setup but it's going to be a dog in most circumstances. Probably end up so disappointing you would end up the car. Just wouldn't be any fun anymore.