That is excellent information/facts, Dave. Too bad it does not show post-1955 261s. However, the later 235 and all 261 crankshafts were most likely similar in weight (maybe even being the same crankshafts after around 1957/58?).
Have you ever had a problem putting a 216 balancer on a late 55 or later 235? You have probably worked on more of these engines than most people here.
I have twice used a a 54/55-1st 235 balancer on a 1959/60 261. No problems so far, but I have only run one of them about 15,000 (most miles at 60+ mph). Those balancers' weight difference would be about 5%.
The weight difference between a 216 and a later 235 is about 24%. That might be significant.
