Use the 6 volt starter with the 216 flywheel and bellhousing. The tooth count on the flywheels is specific to each of the two different starters, and won't interchange. The 6 volt starter will be just fine living in a 12 volt environment, as long as you aren't grinding on it for long periods of time trying to get started.
I'll have to let those familiar with the car motor mounts answer that for sure, but- Your 216 mounts on the plate that sticks out below the timing cover, right? Does the car 235 have holes drilled in that plate? If not, you'd need to drill some holes, or swap that plate (which requires pulling the cam, if I'm not mistaken).
Does anybody know if the car crankshafts accept a pilot bushing for a manual trans? I would guess that all the crankshafts are the same, but I'd love confirmation from someone who actually knows.
