Welcome to CHR, Tazz85. Like Mike/34_40 says, I'm not sure you're going to find a direct bolt mount between the '69 Olds and '80's S10. There may be something out there, but Olds/Pontiac/Chevy did their own things back in the day. You might check over on one of the S10 forums for V8 swaps into S10's and find some ideas. Google "S10 Forums V8" or "S10 V8 Swap" or any number of similar tags and there's lots of information out there.
I'm not a big fan of the S10 frame swap idea, especially for classic iron like a '40 Truck but to each his own. In the hot rod arena you can have a righteous build that's drawing a crowd, but as soon as you say "S10 Frame" folks tend to say "Oh that's nice...." as they turn to walk away. Now that's just my opinion, so don't let me affect your plan, but a friend who has a hot rod & muscle car shop in New Mexico posted this picture on Facebook this morning, and it fits for me....

S10.jpg