Looks like a great tire. However, I don't think it will fit.
It's narrower, and not as tall, which is fine, However, the 1" smaller rim diameter would make it impossible to mount.
Treaded vs Stock:
height: 11" vs 11.5"
width: 6" vs 6.5"
rim diameter 5" vs 6"
(here the stock Vega tire for reference: http://www.tsracing.com/store/showdetl.cfm?&DID=7&User_ID=5100649&st=5648&st2=-36608127&st3=-74377678&Product_ID=5926&CATID=3)