As for-Should you dyno it or not? My first thought is I need to raise my prices-$900USD!!! Thats almost $1300CDN! I charge half that much guess who the dummy is?
I've done that for another one of my vehicles, it was much cheaper and a good learning experience. l also found out air filters can rob around 5 hp shown on the chassis dyno.
Those calculators say a 275 hp 340 duster should do low 13's stock (12's if you believe a stock 340 makes more hp), funny how math (based off what ?) is considered more accurate than a purpose built measuring tool that cost idk $100k + ?
Here's 318willrun's 14.04/96 mph 318 4bbl, headers, small summit cam, pocket ported, 2800 rpm stall and 3.55.
He did run a 13.978, that is impressive for the cheap setup, if my car can achieve 13's I'd be happy. Also looking at his old videos, 318WR port jobs are shinier than mine, but mine being rougher might be a good thing, plus I think I have removed more material to shape the ports and guide bosses a little better.