Get some plain ole cork valve cover gaskets, and while the valve covers are off, get rid of those weak ass stock springs (you'll thank me later).
Then get a FelPro TCS4590 timing cover gasket kit. While the timing cover is off, do my oil mods and replace your timing set with a POS stock replacement aluminum/nylon unit. They're only good for 100,000 miles or 25 years. Port the oil cooler adapter while it's off too.
Next, drop the oil pan to remove the timing gear teeth. While you're there replace the stock pickup with a Melling unit that doesn't have a trap door. Before tightening it down put a blob of clay on it and push the pan against the block to check the pickup height. if it's good, use The Right Stuff instead of a gasket. If you feel safe swapping out a rear seal, pull the cap and do the job. Use The Right Stuff on the side seals with a pipe cleaner as re-bar. Put a THIN film of Yamabond along the backside of the parting line where the cap meets the block.
Personally I'd never attempt a rear main seal job with the engine in the car, but to each their own.