I'm going to guess the OP has crankshaft issues with his new engine. A cheap method to build a 383 Chevy is to turn down the main bearing journals of a 400 crank to fit in a 350 block. Easy to do and mess up. The turned down journals also need to be heat treated to the original hardness or the engine will not live very long. Another option is to bore the main journals of the 350 block, we called those suicide engines. Guaranteed to blow up in a spectacular fashion. The best method is to use an aftermarket crank, it's made to be used in a 350 block. Built a few of these back in the day. My favorites to build were 331 and 311 mouse motors.