are 250 and 292 chevy balancers interchangable?how many different 292 balancers did they make? need some feedback please. thanks

Well yes and no. Physically, I guess the 250 HB would fit on a 292, but the larger rotating mass of the 292 needs the bigger balancer to smoothe out its operation. Most early 250 crank snouts were not tapped for a retaining bolt like the 292 and SBCs. The stock 250 harmonic balancer is smaller and thinner than a 292's HB. 292 HBs can have 2 or 3 grooves for fanbelts integral with the balancer, not a bolt-on like the V8s. Santucci lists the 3-groove unit as GM p/n:10141202.
There are also after-market fancy things like fluid-dampers, but I have no experience of these.

one other thing to watch out for, i have found the timing marks to marked at different location depending on the year of motor. if it is different i just add it to the new one with a file and paint the line. tom

I have run a 250 damper on a 292. The problem I encountered was, it slipped the rubber bonding the damper together after one run. It would also do this to a regular 292 damper. They would last 4 or 5 runs. I am presently running a 8 in. damper for a 350 v8. I first used a used one, it lasted a season before slipping. I installed a new one and so far it has not slipped. On both the 250 and 350 dampers the timing marks do not line up. It must be remarked for the 292. Hope this helps.