Tranny first gear combined with rear gear help

hey guys,

i just picked up a t5 out of a 90 mustang to use in my 71 scamp. The beauty of the overdrive will be awesome since this will be primarily a street car, but my question concerns performance. The car will have a 340 and the rear is an 8-3/4 suregrip that will be set up with 3.91 gears that i got at a great deal. The first gear ratio of the T5 is 3.35, and im wondering now if im going to have traction problems and be blowing up in smoke every time i step on it off the light...I have a buddy with a mustang II that has a 302, 4.64 gears and the same T5 as me and he says he has no traction problems of that sort, and i see lots of guys with mustangs running 4.30's with their t5's...what do you guys think? I am I okay with 3.91? should i go to a higher numerical ratio or a lower one? If i could go higher i would love it since id have a ton of giddyup and that overdrive to cruise at low rpms....lets hear what you guys have to say on this as im all ears8)