Lee Chapman is the fellow you need to contact for Mag Wheels. Please tell him you discussed it with me.
For your information, I sent him an Email a month ago and did not receive a reply. If you don't receive a reply in a week or two, give him a call.
Look here for his web page:
http://www.leechapmanracing.com/
I discussed it with him recently, and he was going to make some either this winter or next winter.
I believe a T-140 would use 8" front wheels, and 12" rear wheels. A 140 uses a T-70 front wheel of 8" with 2.5" back space, and T-70 rear of 12" with 4.5" back space.
A T-142 wold use 10" front and 14" rear wheel widths. A 142 has an extended front hub face that allows use of a T-70 rear wheel of 10" (4.5" back space) to fit. Rear wheels use the same 4.5" back space as T-70.
The above is all just my best guess. I have a T-140 so am pretty sure of that model and the T-142 wheel combinations are in need of confirmation.
Can you confirm your front hubs have the wheel mounting surface almost flush with the spindle end?
David