Flywheel is not able to be put on backwards. The bolts only line up one way. Get a dial indicator on a magnetic base and check the crank runout yourself. Check the rear main bearings for excess clearance (loose). No new block that might be missing a galley plug right? Oil pan gasket leaking bad enough will also get into the bellhousing area. It's difficult, but pressurize the oil pan air and see if any air comes out the back of the oil pan. That will check your rear main too. You will burn up a rear main if the crank was not undersized and you install a repair sleeve. Chev makes special oversized seals for the crankshafts that need a sleeve. Inspect the sleeve you installed closely for being installed all the way. Check with the parts store you bought the sleeve from. See if they have an oversized seal for your your engine using a sleeve. Pull rear main seal out (again) do both radial and lateral runout measurements with the dial indicator you get. Inspect the seal you pull out for damage, lip seal condition and garter spring location if it has one. There are a few types of rear main Teflon, rubber, etc. Use an orange or black Ford seal. You got a zipper on that momo now. Good luck