differences in 904's?

i am in the process of *helping* to rebuild my 904...a couple things, the rebuild kit that i got for it only had four clutches for the front drum, but the trans had five... and when we got the rear clutches/drum assembled, it was way too tight. i had to get .015" milled off the retainer ring, it seems to work fine.
so my roommate/tech guru said he was doing research and found that there is two or three different stock "stages" to the 904's. can anyone confirm this? mine supposedly came from a 77 fury wagon with a 360 2bbl so i guess it might have been a heavy-duty unit? would that explain the extra clutch needed in the front drum? maybe a tow package? the stock converter it had was real tight with a seemingly low stall speed (around 800rpm maybe?).

anyway, just looking for some of that old-skool interchange knowledge....

thanks!
-tim