OMC ball gears, intermediate housings, etc.

[Bill55AZ]

Where do I find the one true and accurate source for interchange of intermediate housings and shafts? I hear that the actual outdrives are almost universal, but that the intermediate housings underwent some changes, some good, some bad, BUT that the housings can be swapped around as a complete unit (with correct shaft/coupler according to brand of motor used). I have a 70 IMP with damaged intermediate housing, and an entire 72 drivetrain, and want to use the 72 intermediate housing (with tapeded roller bearing, a one year thing) until I can find a better unit that takes the 73-77 ball gears/shaft/ etc.
Also, is it a bad thing to have the ball gears mismatched? The one on the outdrive is new, the one on the 72 intermediate housing has about 25% wear.