How interchangeable are Volvo penta outdrives?

[tuantom]

Does anyone know of any limitations, other than the lower gearcase ratio, to combining Volvo 200,250,270 and 280 (not sure about 290's or dp's)? The upper, intermediate and lower gearcases by appearance seem as if they can easily swapped from one model to the other. Do the internals match up as well?
After my old 200 unit chewed up its lower gears, I aquired a complete 270 outdrive with a 2.15:1 ratio; but, being I'm running a 351, I'm going to put a 280 lower with 1.61:1 ratio. Everything fits together very nicely- Am I overlooking anything, or is it that easy.
Thanks,
- Tom