I also picked up the wheels from the guy who makes the plans.
One major problem I have found is the level of grip at speed is so high my little girl (2) is nearly thrown out, I currently have the car sat on my roadster build table trying to work out roll bar and seatbelt arrangements!
Have clocked her at 4mph in 1st gear and 10mph in second... which for a 2 year old is too fast
(especially when she doesn't quite understand steering yet
)