The guy that said he fit a T4 axle into a T3 said you needed to do some minor modifications to do so (lock nut etc...). Dura Blue wouldn't be interested if thier axles could be shoehorned into other aplications. All they would care about is fitting their axles to the machines they were designed for. That said, I wouldn't bother with the t4 axle as they are rare anyway.
Today I pulled out the T3 carrier and put my spare 04 YFZ450 axle into it. The bearing surfaces are a match, length and diameter. It fits snugly into the carrier. The Sprocket and Brake hub splines were a different size though. It would require the use of YFZ hubs if this mod was to work. I'm not stripping my YFZ to get to the hubs so this little experiment has come to a grinding halt.
My toys 85 KXT250A2, 85 ATC250R, 85 Tri-z 250, 06 LT-R450, 04 YFZ450S, 07 125 typhoon x 3, 06 FPV GT.