this horse has been beat to death , but------

I have had a rear mainseal leak since day one , I have finally found out why, after 3-4 times trying to fix it .
The main seal cap is not made right, or the bolt holes in the block are offset from perfect, or the crank is setting in the block crooked . Don't think it the crank cause all pistons were exactly the same deck heigth when built , if crank was crooked one side would be off , compared to the other side. I installed the main cap after cleaning it up w/o the side seals , letting it center itself on the crank , ( no bolts) , one side of the cap is way closer to the block than the other side . I redrilled the bolt holes out bigger and checked the bolts , they (allen heads) were .005 bigger than stock , slightly adding to the problem.
I still haven't figured out how to seal the cap on the sides , w/ the engine in the car ,
getting the whole mess clean of all oil would be a ***** , not to mention how to get sillicone up in there to seal it from the outside.
I have found a billet main cap that is offered by an old funny car racer, and not like the current ones on the market, ordered it this morning. If its the same way , sealing the sides will be a bithch , 73 yrs old and laying on a piece of cardboard in the floor aint fun any more !

Sorry for the long rant m "more to come !"

If you replace the main cap, it has to be remachined to match your engine - align bored... You will have to pull the engine out and strip it down to the block to get it machined... When they machine a block, they rough bore the caps and mains, then bolt them together and align bore the crank bores so they are all lined up properly - that's why you can't mix and match the caps and have to keep them in the proper order that they were machined on the block....