12 second 340

Well if it is i imagine you would have the high compression unit. Sometime in 72 they switched to the cast crank LC in the hole pistons...4 valve relief. The balancer should tell the tale. Hell even if it is a cast crank and in the hole pistons its not the end of the world. Pistons can be changed.......If its a cast crank thats okay too. Those things should be okay for up to 400 or so hp. Probably more.
It was eatin at me when i got mine to know exactly what was inside so on the advice of a friend we took it out and i tore it down to find exactly what was in it. If you want to build it up your going to have to find out sometime :) ....a good winter project...at least take the heads off and see what bore size you have and if they are 4 valve or 2 valve relief....you might be :o