A 216 with a neoprene seal in it is a guaranteed leaker. The only type of rear main bearing seal that was ever used on a 216 was a rope seal, and the only one available currently that has any chance of working right is the Best Gasket brand. Follow the instructions that come with the seal exactly- - - -taking any shortcuts or ignoring the instructions will probably lock up the crankshaft. Both rod and main bearings need to be shimmed to as close as possible to .0015" oil clearance, and the spray nozzles in the oil pan need to be checked and adjusted for proper alignment so the rods will get lubricated properly at any speed above idle. There is also a fixture to check the depth of the troughs in the pan to keep the rod dippers from hitting them.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!