ok i have a 1973 307 that came out of a nova it was built by jegs and i have no clue what was done other than a race cam.i replaced all the gaskets and water pump,oil pump,fuel pump. i have a 1985 gmc truck that has a 350 in it that is wore out and wont pull its self out of its own way. so i wanted to replace it with the 307 thats alot fresher than the 350 but i cant get the timing right the top dead center mark on the harmonic balancer isnt right or even close .i pulled out #1 spark plug and turned the engine over with my finger over hole and when compression blew out i figured that was top dead center but it still didnt fire and run right,it backfired out of carb .... what to do ...im lost  

sounds like youre 180 out.Bring up #1 to TDC,remove the distributer cap and make sure that the rotor is pointing at #1 on the cap.If not(with #1 at TDC)pull the distributer and reinstall with it pointing at #1 on the cap..see if this helps