KillerG, try the engine out, in the interests of science. From memory (correct me if I'm wrong) the Hyper has a three needle carb, so mid range should be discreetly adjustable.

The Tower .46 muffler (or any OS .46 and clone muffler for that matter) should bolt straight up to that engine.

If you go ahead, try an APC 11x6 or an APC 12.25 x 3.75 out and get a tach reading. Let's see if she can get into the 13-14k region!

Keep us posted.