2 750s on a t-ram on a 400sbc will be very soggy driving around. These intakes are designed for hi rpm, lots of gear, hi stall converter/4-speed light weight cars.
UNless you want this set up for looks and not go... then ok, but a good single carb and intake is a lot easier to live with.
The 2-3 10ths may be possible depending on your setup, you will probably get a little better mph, but it will kill your 60's,
In my opinion, you could better spend the money elsewere to get the same or better et increase.
IF you still want to do the t-ram, a pair of smaller carbs in the 600cfm range would be easir to live wtih...