340 crankshaft info needed

.............I would get it balanced.........keep the unleaded heads....u need a neutral balancer....kim................
Yup, the balancer can come off any internally balanced small block. I would match it to the timing cover and crank pulley you're using but if you find a nice one, you can re-mark the timing slot and egg out the pulley hole. The 1.88 valve 587's and 1.88 valve 915's (J heads) are real close so I would swap them unless you plan on some major changes.