Timing question, Searched didn't give me much help

[xero_gto]

I know this is asked atleast 100 times a year, but i couldn't find much in the way of my situation with the search function.

Basically what im trying to do is ensure my initial timing is set correctly. I know the truck starts and idles fine, has some blow by coming from my breather. As soon as you put it into gear it idles horribly, drops to around 400 from 650-700rpm it shakes, and while under a load and accelerating it has a pinging coming from the hood. Which makes me beleive the timing is off. both initial and full advanced. I got a timing light from summit, and im trying to figure out what i should be running. Chiltions say's 4deg BTDC for a 70 350 with points, but the previous owner put a HEI in the truck, he also mentioned the engine was from a 74 i beleive. So i looked up for the first year HEI in the chiltons and it says 8deg BTDC. I'm trying to figure out if thats right considering im running long tube headers. have an edel dual plane intake, and a summit carb. Any input or just a WAG (WILD A** GUESS) would be appreciated. Thank you.