I'd imagine a standard 3kva transformer would be fine here (depending on the connection on the unit) but prob best to confirm with Grainfather so you don't blow any circuits
Edit:
Actually scratch that, sorry, head was in work mode for power tools, this won't work
I wouldn't trust any of them i would bite the bullet flog the 120v 60hz machine and either buy a used UK model or new if money was available as @MashBag says you are running this 60 minutes at a time to me its not worth the risk.