Have some of you guys out there experimented with taller than standard tire sizes in order to get a lower effective ratio when using a V8 conversion ???

I doubt you can make enough difference with tires to bother. Tires that will fit the car without radical fender surgury will only change the ratio by 5% or so, and nearly all of them will change it in the wrong direction. The stock sized 165SR15 tires are actually pretty tall (26" in diameter).

When the GT flares are used will a 29" tall tire fit ??
(255/55-18)

29" dia. tires would yield awesome 0-60 times in a V8 application, using 2nd as 1st, while keeping just under 6k. My tires are like balloons at 195/70-15, 25.75" dia, and hit the front valence edge when I lift the front, but my speedo's pretty accurate, which I like, and the gearing's good for highway cruising.
Ed

What about the final drive ratio. Does an 8/31 final drive gear set exist for the 901 tranny ? Or must one upgrade to the 915 tranny to do this ?