rear Main Seal noobie question

That's about it, and no you don't have to split the engine and trans.
One suggestion I would make is just to offset the ends of the seals from the main cap and block about 1/4 inch (where the main cap and block meet, rotate your upper seal half so you have about 1/4 inch sticking out above the block surface and match that with 1/4 inch in the cap) like the picture.
Then just a touch of RTV where the seals meet, and a small bead (a film basically) where the red lines are in this picture so oil can't get out between the bearing cap and block.