My 383 is weak!?

I think you might have a little different result than you think... If the pistons were "10:1" but they were installed in a '69 383 without the block and heads being blueprinted, and with the common head gaskets, you really have compression down around 8.8:1. Add to that the MP cam which if not degreed is probably off, and the 2. series gears, and it's going to be sluggish. You need to take compression readings first and post the results.