Timing Chain Cover Replacement

Getting ready to replace my timing chain cover due to a leaking gasket. Picked up a used one anticipating heavy corrosion behind my current cover. The used one I picked up is in great shape, hell its even date code correct! But after cleaning it up, I noticed the block mating surface isn't flat on one side. I put a straight edge on one side of the cover and can rock it back and forth pretty good. Is this a really big deal when I go to re-assemble? Should I use some type of sealant in addition to the gasket? Any tips or tricks would be greatly appreciated. Thanks.

Car is a '72 plymouth duster 340