I recently purchased an Chevy 355 that is in need of a rebuild. I took it to the machine shop to get the block checked to make sure it didn't have any cracks. I also took the crankshaft to get it check out. The guy at the machine shop told me that he doesn't recommend using the crankshaft because the mains have been turned down 30 and the rods were turned down 20. Can I use the crank or is it safer to purchase a new one?