I was asked recently by a board member about this subject. This is a mod to supply additional oil volume to the rear main bearings and is usually only recommended for engines that will operate in the higher rpm range. I think MC can do a better job of describing the details of the mod than I can since it has been quite a while since I did this myself and he knows much more about AMC blocks than I do.
I wanted to use the the stock metal valley pan gasket with my engine so I used brass fittings and a 3/8" steel line to make a low profile version that cleared the stock valley pan intake gasket. If I recall correctly I believe the 2 holes are drilled and tapped to 1/4"npt. The photos below show the details of my setup for anyone interested:








editied by jeepsr4ever