I am in the process of installing a 2.8L chevy and T5 in my spitfire. My current differential is a 4.11 which I did not like with the original engine/trans combination and since the gears for the Camaro (donor car) were 3.42 I would like to go with the GT6 differential. This will be a daily driver, as long as it is not raining, so my thinking is that the GT6 diff will handle the HP and torque of the V6 which is only 135/160. I have friends in Montana and would like to be able to go 80 mph on the highway as I'm driving to their house. This was impossible in the Spitfire with the 4.11 gears.
http://cgi.ebay.ca/Triumph-Spitfire-GT6-rear-end-rare-3-27-ratio-warranty-/310267984581?pt=Motors_Car_Truck_Parts_Accessories&hash=item483d69bac5
came across this while looking for other stuff.hope it helps you.
Thanks everyone..........Found what I needed on ebay........