merc lower interchange

I have a 1975 50hp merc 4 cylinder. What lowers will interchange with this I dont have a prop yet so if the gear ratio is different thats ok if it will fit otherwise. thanks

I don't know, but I'll keep an eye on this thread. I've got a '74 and a '73 ( I think, I never looked the numbers up). Motors look very much alike. The one I run has had an extension put in, I assume from short to long. The spare is a long.
I bought a new prop for my good motor shortly after I got it. It was different. The new prop was not as long (linear to the shaft) as the old one. I got to looking at the spare motor and it had a washer between the hub and the nut. The new prop requires the washer to fit my good motor. The prop that came with the boat also fits the spare motor without a washer. So, there is some difference there between one model and the next concerning prop fit, if nothing else.