I had a Mopar brand 2.77 low gear set installed in my old pump gas Duster, that worked well with 3.73,3.91, 4.10 and 4.30 running 315x60x15 M/T Et Street Radials and the same size ET Street bias ply tires with that 400 stroker motor with both the 4.25 stroke crank and the longer 4.300 stroke crank later up
That car ran 127.+ MPH with the Eddy RPM CNC heads and pickup to 134.+ MPH with the M.W. size Indy SR with a Indy 400-3 intake and several different 1050 CFM Holley Dominator carbs corked up with the air cleaner on using 92 octane OR pump swill from Bend shruggy
I haven't used the TF270 heads yet and I don't know how they compare to the Indy SR M.W. heads non ported work
The 4.250 stroke will move the mass a lot easier than the SB motor will with a 4.00 stroke in a SB 340 or 360 motor twocents
Good luck on your new build thumbs

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)