I have a 1 piece rear main seal aftermarket BBC block. I am using a Milodon aluminum timing cover (Gen V 10 bolt cover) currently that has the groove on the back side for the oil pan gasket to sit in.

I am thinking about changing to a belt drive setup for the cam but most of the offerings fit the older Gen 4 blocks with the flat oil pan gasket sealing surface on the timing cover.

Do I need a custom oil pan to make this work or can I just use a Gen 4 oil pan and gasket? Not sure if the oil pan gasket is the same at the rear main cap between the 1 piece and 2 piece rear seal blocks.

Hope this makes sense.

Not sure on the Gen V but my old Gen VI the rear of the pan was different and when I went to Mark IV belt drive my builder just welded an piece of flat stock to from of pan where cover goes to extend the lip for it to seal up. It worked great until I broke the block. I bought a Dart block and sold the pan.

I was gonna have a piece machined to weld to the front of my old pan to use with the Dart block but found out the rear of the pan wouldn’t clear the rear main cap of the dart block also.

My experience with the Gen V block has been that it's a real pain in the azz, on several issues.
Terrible idea, but at the time it was the only big bore block available.