A DIRECT SWAP '71 904 for '70 904 plus... ???

Hi, I am getting ready to swap on my 1969 Valiant 100 2-door post with original 170 Slant six the currently installed Automatic 904 (part # 3515804 ALUMINUM bell housing out of a 1971, what car exactly I don't know, also has "0744" on bell housing) for a very low mile Automatic 904 transmission from a 1970 Valiant 4-door which is also a slant six but the 225 size (it is the original transmission in that car but haven't gotten the part numbers off it). Will the 1970 auto 904 bolt right up without anything additional being done after pulling the 1971 auto 904 currently installed? Any bell housing or internal parts issues with the new transmission being from a 225 slant? Any benefit to keeping the current lighter aluminum bell housing (weight)? I am wanting to swap the transmissions as I don't know the history/mileage of the current 904, the new one will only have 10K gentle miles on it AND I will already be swaping out the driveshaft and 8 3/4" sure grip raer from the low mileage car to my 1969 so think I should just do it all at the same time. Can anyone also confirm that the driveshaft & 8 3/4 " sure grip will bolt right up without any modifications from the 1970? The 1969 has some smaller non- sure grip rear in it currently which is date coded 11/5/70, so I think it probably came out of the same car as the current transmission in it. Seems to me that if the new transmission bolts right up that the new driveshaft & rear should also bolt right up - all from the same donor car so driveshaft length will be correct? Sorry for so many details but want to be SURE & give enough info to you tech wizzards. Paul Charleston, WV