OT: An A-body t-bar is shorter than an B/E body t-bar.
Both length and diameter factor into the spring rate.
A b-body bar of the same diameter will have a bit lower spring rate.

On topic:
I don't know why you all are insistant this gentleman will be unhappy with his tbar upgrade considering his base and objectives. Take a look at the tires, rear springs and the types of use he has in his objectives. The tbars and swaybar selected will both noticibley reduce the roll he is experiencing. Could it be even higher roll resistance? Sure. But for his combination there are other places to make changes that ought to go with higher roll rate. Plus if some drag strip launches are part of the plan, which it seems to be, then staying on the soft side with the t-bars can be used to advantage.

For a good launch, 90/10 on the front shocks would a useful function. Not many companies offer that with an option to go back to near 50/50 for the street, so that will limit the options. On the drag race forum you may find some people who know off the top of their head. On the rear, it would pay to measure the shock length at reat and at compression and extended as it may not fall in stock parameters any more.

Finally, an alignment that is more favorable to the handling characteristics will make a difference too. Especially if you are going to modern radial tyres that tend to prefer a bit more negative camber than bias and cross-plies. This is true even for general use street tires like the BFG Radial T/A. Set the ride hieghts, a bit negative with the camber, and 2-3 degrees positive caster if you can, and then a very little toe in (static). The higher rear may make it harder to get even 2 degrees caster, but each car is a little different, just do the best you can.