88 chev 5 speed trans

My 88 chev p/u with a 350 and a 5 speed trans will no longer go into reverse. All other gears are fine except every thing seems to have been moved just a little to the right. In other words, when I am in 1st it feels like the shifter is just a little further right than before. I removed the shifter and I noticed there is a roll pin in the bottom of the piece where the shifter ball rides. This roll pin is not driven down flush but rather is up maybe an eighth of an inch. Wondering if this pin sheared off on the bottom. Anyone have any ideas? I've never taken a transmission apart. I have located a transmission that came out of a 1990 Kodiak that has a 454. Anyone know if these 2 transmissions are interchangeable?

I have some bad news about this transmission,you cannot get parts for this and are hard to find used if it is a half ton.The book shows how to take it apart and parts are not available from GM.My father tried once for a bearing and dealers said no parts listing for this bearing.Probally the transmission out of the Kodiac will not fit and call a wrecking yard since most have an interchange book called a hollander