If it is a stock 400 crank ground down to fit in a 350 block and if it is externally balanced it would have a weighted balancer and the stock crank would have a pin for locating the external balance flexplate on the rear flange of the crank. If it is an aftermarket crank and internally balanced you could possibly contact a local dirt track tech guy, alot of them have access to a cid pump and you could verify closely your cubic inch that way with out disassembly.