You don't need muffler pressure, but it does eliminate changes in mixture as the fuel level is lowered in the tank. It's a simple measure to drill the muffler and add a tap.

The nipple on the crankcase is a drain for excess oil that gets into the counterweight chamber. Just add a piece of fuel tubing to let the oil drain out the bottom of hte cowl.

There are no other muffler options available from O.S. We're not familiar with any after-market accessories for the engine.

Any good-quality airplane fuel is fine. We strongly recommend a synthetic/castor blend for best performance. Your fuel should be fine.