Talk to them before deciding on which gear ratio, I tried from 3:73 to 4:30 in my old pump gas Duster with a custom built 10 inch Contintental converter for that motor, 517 C.I., 612 HP at 5500 RPM with the low deck six pack with 440 six pack carbs.
That stupid car ran within .03 ET, high 10.40 E.T. in the 1/4 mile,and very near the exact same MPH in the 1/4 mile with the 315x60x15 M/T ET Street radials using all four rear gear ratios, 3:73,3:91,4:10 and 4:30
My message is those long stroke motors with small stock like heads on pump gas make so much torque and HP you may be very happy with 2.76 to 3.23 gears in the rear
I ended up using 4.10 after I bent the 8 3/4 housing bad enough to need replacing, I used a truck Dana 60 and had it cut down to replace the 8 3/4, no more problems after that