1st gear ratio is a combination of gear teeth counts between the input shaft, the countergear, and the number of teeth on 1st. The diameters are specific, so changing gears requires a slight change to the mating gear, so as a result, most gearsets are sold in a set consisting of 1st, 2nd, 3rd and a countergear and input shaft.
Other than the very early non-WC gearsets, the lowest T-5 gearset available is the T-5Z spec with the 2.95 1st gear. Buying a real tremec set is VERY expensive, although it's a bit more manageable with the aftermarket gears many are making these days. Astroperformance is selling a Z-spec countergear for $100 for example (aftermarket).
Add up the cost of all the gears, and it may cause you to rethink it however. Rebuilding T5's used to be cheap, but now it's not anymore.
I have a parts T5 that I'm strongly debating a 2.95 gearset build with, but I should really go with an astro performance build.