What was the plug you were using E-3???
Small cam will kill an engine with vortec heads, even though 170psi is not that much on the compression tester. Most I have gotten by with 383" on pump gas with vortecs is about 10.5:1 CR = 200psi and a big cam at .050 230-240 narrow lobe separation 104*, intake on 100* and a fat carb, and timing at 25* full advance, this engine made about 475HP at the rear wheels. Plugs were marine R43LTS. I buy them 500 at a time if you need them as I use them in all of my crate engines. They retard timing and run cool with crappy fuel and they don't burn engines up unless folks get stupid with timing and lean jetting.
Anyway most folks don't know the spark plug can change the dynamic timing of an engine +/- 5*. That is why Cup engines used to run extended plugs for qualifying an retracted for the race. Most people say it is the heat range but these plugs had the same # heat range they just made combustion happen faster as well as heating up the cylinders super fast.
It also looks like the pistons were touching off on the heads as they are super clean in that area.
On the chassis dyno, I always check timing when cars come in the door. On 602 / 604 Crate engines I drop timing back to 25* after the initial baseline runs and start my tuning from there. I have found there is about 20-30 HP in getting rid of the extra timing that impedes the engine from working the way it was designed to. Once folks wake up and realize that timing advance is a tool for crappy fuel and PI$$ POOR engine design they will come to understand how to make an engine run efficiently.
If you need some good pistons for your engine I would recommend using Mahles HT piston as it is superior to most economy forged pistons on the market.
If you are running standard bore 350 I have some super nice ones coated up and everything that should work up to 500HP pretty easy, I use them in 550HP road race engines and get a year out of them. In a street application that should be 50,000 miles, if the timing and fuel is right.