Gordy, would your friend consider changing the 3.90 rear end to a 3.38 ratio? My thinking is 3.90 x 4.03 is 15.7. That is a really strong first gear ratio. 4.03 x 3.38 is 13.6 and at that point we're getting somewhat closer to the 12.08 the GM engineers designed the truck for. 3.08 would be a perfect first gear ratio, however I'm not sure a ring/pinion set for the rear end is available in that ratio and there are some 3.38 gears available. I mention this because 15.7 is going to have your friend wanting to shift to second pretty quickly (maybe not even completely through a city intersection) and a ratio of 12 will allow him to drive around a lot more comfortably.
I mention this because (a) he is spending the money to have a T5 rebuilt and (b) I suspect he wants to enjoy driving this truck and (c) I've had friends who have ended up with a truck which had nearly a 16 overall first gear ratio and they grew to hate it because it is irritating unless you're on a farm pulling a trailer around or something. Here's the thing: in the T5s with a first gear of 4.03 the second gear is 2.37. 2.37 x 3.90 = 9.24. Taking off in second gear with a ratio of 9.24 is fine if you have a big V8 but if you have a 235 it might not be the best choice...especially in city traffic like Anaheim or LA. You need the right overall gear for the most enjoyment is what I'm saying and the GM engineers knew it.
Just a thought, Gordy.
