I am a BIG proponent of the 904, I have done the change twice and both times I picked up .5 and 6 mph with the change which would make you a 13-oh car. I would also be suspicious about the converter, I think you stated you are running a 10 inch that stalls 35-36 hundred. This stall is really high for a short stroke 318. I think tightening up the converter will push your mph up a lot but wont help the 60 foot unless its slipping so bad that you aren't utilizing the torque peak. The original combo you ran sounds like a well thought out combo and I would look elsewhere for your ET. The problem with 3.31 stroke combo is torque, or lack thereof. I ran a 273 that had similar problems, but I was able to get it right although the converter company was local and they reset the stall like 5 times to get it right. Once it was right it worked great! Good luck!