904 Transmission Fluid Recommendation

Dexron III or Type F. If the car sees limited use or isn't being raced regularly, you wont really see the advantages of using synthetic fluids. The specialty fluids sold by TCI, B&M, T/A etc.are more of a gimmick than anything else. Type 4 fluids(dex4, Mopar ATF-4 etc.) have a friction modifier added to them that is intended to provide softer smoother shifts(contrary to shift kit equipped cars). Any ATF can be used in any transmission without causing damage. It will only change, if at all, the shift firmness. The only exception is fluids designed for CVTs which are a different animal. The auto manufacturers started to recommend type 4 ATFs a few years back to 1) soften the feel of the shifts. 2)To mantain the quality of the ATF that was being put into transmissions that were failing under warranty. No ATF can overcome short comings in product design. 3)The manufacturers were all competing to advertise lower cost of ownership throughout a vehicles lifetime & thus extended the recommended fluid change intervals. They believe they can achieve this with the use of synthetic fluid.
I've used type F in my cars for decades & like the way it shifts. NEVER had any problems. I have used it in vehicles with conventional coverters, race converters & even lock-ups with no problem. I change it every 30,000 miles regularly. It's cheaper than synthetic but a little less available.