Ed,

Yes, the later flywheel (and clutch assembly) that works with a 12 volt starter will bolt up inside your 216 clutch housing.

I recall having a problem with the clutch throw-out bearing but I do not remember if I used the longer or shorter throw-out bearing.

I went to 12v when I first put a 1960 (12v) 261 in my 54 Suburban. I am now swapping back to 6v.

Tim