My guess is somewhere between 11.80-12 flat initially.

I had a pretty similar combo years ago in my duster( which at that time with me in in was 3450 pounds( bench seat interior, all steel and a 300 pound driver)cage, etc, etc.

Same headers, different muffs, 248/258 crane cam( way to little), airgap, 727, 4.10 gears, 3500 10 inch convertor, several different carbs, a little more compression, and similar eddies( mine maxed at 275 on the intakes, so likely not quite as good) the car went best of 11.69 at that time, with a lot of fiddling around with it.

I went with 8 inch convertor, fully ported heads, 260/266 flat cam, changed intakes, and raised compression,( 12-1) hair less weight and picked up a whole second the following year. Those saying you are going to run 10's with your current combo will soon see it wont, but you have a nice deal there, good luck. Should pull hard.

With that cam and compression, and other factors, hook, convertor, etc, etc, i suspect about what i sad above at somewhere around 113- 114 mph...