70 318 with 340 internals/Cyl Head

All,

I'l looking seriously at a 73 Duster that has 70 340 internals and heads in a 70 318 +.030 motor. It also has a 340 torker, some mild cam and headers. What exactly kind of brew is this and what is it's output potential? What kind of comp ratio are we talking and cubic inches? It has a 3800 stall conv and a 3.55 gear.

Thanks,
Marion