So they're basically both just access holes for the flex plate/clutch - One for the socket and one for the barring tool.
Thanks guys!
Smaller hole has a plastic plug with an oring. Thats the barring tool hole. Big hole has a plate that bolts on, its for access to flex plate bolts. Manuals have same setup which is why I don’t beleive there to be any difference.
FYI I dicked around with a dual disk street clutch (at SBs suggestion) in front of a getrag and an nv4500 and it just would not shift. Southbend ended up replacing it with a single disk no frills clutch and gave me some of my money back on top. Point is, if you go SB I’d buy a lower HP no frills single disk and call it good.