I went thru this same scenario back in 1995. I had a 1973 904 that came behind a 318. I wanted to swap in the 2.74 low gear and the wide 5 clutch drum. Doing a lot of research, there were several different variables that had to match before parts worked together. The best core to start with was the 1975-1977 A999 trans that came behind 360 engines. These had the wide 5 clutch front drum, non-lock-up shaft, bevelled back pump, and longer splined forward clutch drum hub. If you could find one of these, all you needed was a 1980-up 2.74 gear set to complete the package. I could not find one, so I started piece parting this thing. I was able to obtain a bevelled back pump & a wide 5 clutch direct drum from a local tranny parts house. These were for a '75-'77 360 trans. I still needed a special bevelled direct clutch drum piston and the longer splined forward drum with non-lock-up input shaft. I got the P/N for the dished piston in the Direct Connection Chassis Book, and the Mopar dealer ordered one. No luck finding the forward drum, so I called Dynamic Racing trans. They knew exactly what I needed, and sent me one. The forward drum used with the 4 clutch direct drum has a 1" splined hub, but the forward drum used with a wide 5 clutch direct drum has an 1-1/8" splined hub. This is the difference that was pointed out at the start of this post. After all the parts were obtained, the trans went together without problems, and still is being run in my low 11 sec 340 Duster. I wanted to build a spare trans, but had problems finding the '75-'77 parts. So I did some more research and calls. Found out that the '78-up parts will work, if I can find non-lock-up components. So, off to the tranny parts house. Was able to find a non-lock-up, bevelled back pump, wide direct drum, and the non-lock-up long clutch hub forward drum. The '78-up parts used a slightly different sized sealing ring on the stator and forward drum, ~0.060", so you have to be careful when matching parts. The non-lock-up pump has 2 balls sealing passages in the stator and the lock-up has 3 balls. That is an easy way to ID them. The '78-up parts seem to be more plentiful, but usually you find lock-ups in everything from '78-up except for Fleet vehicles, trucks, etc. I have an old CarMatic trans parts book as well as one from Delta that I use to ID parts. It gives Mopar part numbers as well as industry part numbers, and some identifying dimensions where required. The 904 is a challenge to build with all the variations, but as long as you have all the info, it becomes an easy task. I talked to Rick Allison at A&A for 2 hours, and he helped me tremendously.

John