It's been awhile but I have made progress. After talking with my tuner and BTC cams a lot I made the following changes:
First - I bought a set of Doug Thorley tri-y headers through Apicella designs. They have DT make a slightly custom set to specifically fit the TCI chassis and tuck the headers up into the chassis. They fit great.
Second - I have a dual 2-1/2" exhaust, no X or H pipe (no room with it lowered), and some generic quiet turbo mufflers. I swapped the mufflers for a set of Flowmaster 40's.
The seat of the pants result was significant! It felt like a nice power boost and of course, was louder. No dyno run at this point.
Next - we pulled the heads (TSP ported 317's with larger valves) and milled them .0035 for better compression. This was in addition to a .0005 cleanup mill from when they were initially ported.
Finally, I swapped to a slightly smaller cam. Had the BTR Stage 3 truck cam, swapped to the BTR Truck Norris cam. These typically add a little in the lower range, roughen up the idle, and do nothing for top end power.
Then we ran in on the dyno again. You can see the before and after runs below. The result - HP increased by 22 to ~348, and torque popped up ~40 lb ft, which would equate to about 420HP and 450lb ft at the motor, at sea level. The increase went all thru the RPM range.
Dyno run here:
https://studio.youtube.com/video/czgsxexLG2A/edit
Bottomline - much more power right where I want it. Those are rear wheel numbers so engine numbers are ~20%-ish higher but then altitude sucks them back down by about the same amount.
I believe the headers helped, and the cam and compression helped some too. Which one by how much - I don't know but I'll guess ~50% headers, 30% compression and ~20% cam, give or take who knows how much. I can say it's a blast to drive and the exhaust noise and idle are rough, loud and rowdy and I love it!