Oil leak problem..

If you use the 90 degree adapter it will eliminate the plate but you'll still have gaskets to contend with. I've never had any problems with any leaking myself except one that came loose. Are you sure your using the correct gaskets? Have you held them up against the block and plate and compared sealing surfaces to see if they look like they fit correctly? Never seen any that use a O-ring but there might be some out there.

One last thought. Is your oil pressure excessively high by any chance?

BTW: Excellent looking ride!!