Muffler? What muffler?
Youz' 911 guys need to get snuggled up a little closer to your motors. When my right ear is 18 inches away from a set of Webers, I don't hear no stinking exhaust.
The 2.7L is a good engine. My total bill for machining (case savers, line hone, crank work, deck & square) was under 500 bucks. If a mag case won't clean up with a line hone, pitch it and get another. A good machinist can give you the bad or good news before you spend the money. A 76 or later case already has the oil bypass mod/larger pressure side included. Just make sure to get the latest & greatest spring set up for the pressure relief/bypass system.