904 Transmission Fluid Recommendation

Hmm ... Let me squeeze some lighter fluid on this smoldering fire pit ...

The A-604 was Chrysler's first , if not thee first , auto trans which had no bands ; it was all clutches .
That alone would indicate the necessity of a unique trans fluid formula , henceforth "+3" , ad seq.

"Type 'F'" was specified back in the 50's , as FoMoCo's Cruise-O-Matic , et seq. , were pan-fed their fluid , necessitating the foam inhibitors , and thusly adding viscosity to the fluid .

ATF Suffix A (Dexron , a one-time GM trademark) was a much different fluid back in the days prior to the 1972 ban on Sperm Whale Oil (which was used as a friction modifier). That fluid would last virtually forever !
Dex II was its replacement in circa 1972 ; Type 'F' was unchanged , and was mandatory on all '76 & earlier FoMoCo transmissions , including the FMX .

Dexron III / Mercon is too thin these days . Has been for 20+ years . When lockup torque converters were intro'ed in the 70's and overdrive automatics became common , the fluid didn't need to be as viscous as the operating heat of the trans was down .
However , extra friction modifiers were necessary due to higher stall speeds of converters ; enter MerCon V , DexRon IV and Plus 3 .

B&M's ATF is essentially Type F . I can't speak for *cringe* TCI's stuff .

I used Lucas "Sure-Shift" mixed with Type F in my 1972 A-904-LA (which reminds me ... it's time for a filtre / fluid change and band adjustments ) .