the stock elbow is like 60* IIRC... a 90* elbow makes life much easier... I get mine from Jeff (snedge)
You can buy fittings that go from the STORM fittings to a -AN fitting and use an AN line. I know turbonetics sells them. You can get them off ebay also.
some of the S300's have a two bolt flange on the oil inlet, some don't. if yours does, you can buy a two bolt flange that has a -AN male fitting on it and just use an -AN line for the feed. -4 is plenty sufficient.
on the drain side... my FIRST "generation" involved cutting the factory 3rd gen drain in half and bridging the gap with hose. it works alright, but I had some issues w/ the silicone hose getting torn by the corrugated steel.
so this time around, I bought another 3rd gen drain tube and cut the original down low near the block where it's smooth so now my hose slides over smooth steel on both ends. use shielded hose clamps, and I don't forsee any issues.
I know ATS uses a longer factory drain tube in their twin setup, but I don't know the Cummins part number, and the setup I've got isn't expensive.
OR, you can just use a 2nd gen oil drain, pull the plug out of the front drain port and use a full 2nd gen oil drain setup.
if you decide to use the rear drain port, you MUST buy a wastegate actuator from Enginered Diesel!!!!!! the original one might fit, but I prefer the simple drive pressure style gates
