I have never built or rebuilt an engine so i hope this doesn't sound to stupid. Can a 350 block from the 70's be used to make a smog friendly engine. Have there been different mods on the block since then to incorporate smog equiptment. I know where a block is from the mid to late 70's and its free. It still has heads and manifold, pan, crank,pistions ect. I know it would be a great learning tool to work on taking it apart and rebuilding after machining. thanks for any help. I am building it for a 91 ta need echeck here in ohio. Dont mind keeping the air clean anyway

 

Here are the differences. The 70 block is a 2 piece rear mainseal and yours is a one piece, you will not be able to use your pan, or flex plate. your block is machined for a roller cam (factory) and the 70 is not and can't use the factory set up. you can get retro-fit rollers though for it. The dipstick is on the drivers side on the 70 block, but it's not a big deal unless you want to use your late oil pan (won't work).
The similarities are they can use all of the same heads (as long as you have the right intake, since they changed in 87 along with the valve covers), trannys, waterpumps (as long as they are the right length so your pullys line up, but the old pumps won't work with a serpentine belt because it needs to be a reverse rotation model).
To answer your main questin though, yes.