All of the 216/235/261/engine crankshafts have a 1 1/4" snout diameter and a 1 3/4" diameter seal surface. Ditto for all the 2nd. generation sixes- - - -194, 230, 250, and 292. Small block V8's also share those dimensions. The balancer/pulley setup I make uses a 6" diameter V8 balancer with a big block V8 2-groove pulley inverted over it. It requires some machining to get the length of the snout right and some work on the depth of the OD. A 250 balancer can be modified the same way, but since the belt driving stress is carried by the rubber isolator ring, I'm not very impressed with that setup. The balancer ring on the V8 damper is not stressed, the way I do it.

Yes, the balancers will interchange- - - - -no, it's not a drop-in swap.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!