tuned exhaust for a lycoming 0320

I'm just having more fun than should be legal and it probably isn't if I
look far enough into the County, State and Federal statues, but I am
never-the-less. I have pretty much followed the Cafe numbers for header
length and the 4-into-one collector. Keeping in mind friendship to my
neighbors, I also included a muffler. I purchased the collector and muffler
from Barnes Stainless and will be purchasing the header tubing, 321SS from
the same source in all likelyhood. A/C Spruce has the tubing listed at
$8.75/ft.
I've made up some PVC headers complete with flanges glued on and am heating
the PVC with a heat gun and bending them until I get the pipes where I want
them. The plan then is to take the bent up PVC to a muffler shop that has a
mandrel tube bender and have them bend up the expensive 321 SS tubing. I
plan on welding in some of the 3-bolt ball fittings to both ease the
stresses and make installation and removal easier.
My plan is to install the stock exhaust, do a hover and check the MP and
then quickly change exhaust systems and repeat. I'm hoping to see a MP
improvement.
I've had this plan in my "Round Toit" list every since I read the Cafe
study.

Dang I sure do like the experimental category. No bureacrats in the way.

Stu