Ive got a 336, its little rear handled brother. I am in the same boat as you. I want to modd it, but no info. I was looking at doing a muff mod first. The muffler is so freaking odd shaped! My idea was to heat up the shell crimp and pull it apart. If the there is a baffle(should be one) drill some holes to get better flow. Also open up the deflector or replace it with a bigger one. It has a magnesium bottom end, but it doesnt look too beefy. I am not sure it would hold up to a full on porting job. Its limited flow air cleaner and muffler might as be a problem. Another idea is a make from scratch a new top half to the muffler wih more expansion room and a better deflector.