(need help)what other lower unit fits 1991 70hp force(706p91B)

[tnbull38310riverrat]

i was in the river easy geared in rpm shot up and no speed are there any pins i need to look for i checked prop its ok got it back on trailer (put it in gear i could still move the prop not to easy but with slip )(what other lower unit fit this 1991 70 force motor that for the help i also have a (115 merc lower unit for sell dont know if it will work with mine havent checked) scott: long time towboater