transmission question

[1980c-10 mybaby]

Hey guys im here looking for some answers on a transmissions setup that i would like to try...... im putting a 305 in my 1980 chevy c-10 and im looking at going with a manual 5 speed with overdrive to help with gas mileage on the highway....... im wondering if anyone has tried putting a newer year tranny on an older motor (which is what im looking to do) i have been looking around ebay has alot of 5speed trannies from s-10 and the pull-a-part close to me has alot of manual trannies as well but nothing from the older years........... so if you could shot me a line and tell me if it is worth attempting or if you have done it and it worked


Thanks again guys