3 speed help on a 1970

[Rmax]

HI new to the site but could use some help.
I had just sold my 63 nova and was feeling stupid when I found this 1970 c10 with A 307 and 3 on the tree up the street for $500.I know its not cool as a long bed but got the little 307 to run and took it home. The 3 speed is done as it has no 3rd gear and sounds like a small war is breaking out inside but the clutch is good.I dont have a lots of money for a cool swap so I was thinking just put a 3 speed back in as I think 3rd is still a 1 to 1 .I found some on craigslist for cheap but wanted to make sure I did not get anything that would not fit. I guess what Iam asking is can I use a 3 speed out of a car? are there differences within the years that I may need to watch for?............... anything that may help
Thanks for your time
R