My guess is it will run about the same, maybe 0.1 quicker depending on the ramps, head flow, etc. Our engines are almost identical except I have a small street roller (248/254 with .576/.582 lift). Mine has run a best of 6.67 (when it was not tuned right yet), but now it usually runs in the 6.70's in street trim with mufflers. I'm hoping to nick the 6.599999's this fall now that I have the fuel curve sorted out.