Rear Main seal

Hi everyone. I found the dreaded oil spot under the car this weekend. The engine had sat for two years before I swapped into my Valiant 3 months ago. It's a 360 out of a 79 Newport. Can the rear main seal be changed without pulling the motor? I replaced the oil pump and pan gasket. Is there anything special that should have been done around the back pan seal? Thanks for any info.