You could do what I did- swap in the whole 400 from a Majesty. Easy swap. The head from the 400 will bolt right on to the 250 but you might want to get it cut to raise the compression. You could also send the ECU out to get re-mapped.
I was thinking of doing that with the 400maj, I would imagine it would be a good increase,,,,is it a whole engine swap with the tranny and all or you just swapping the top end and leaving the tranny and CVT?You could do what I did- swap in the whole 400 from a Majesty. Easy swap. The head from the 400 will bolt right on to the 250 but you might want to get it cut to raise the compression. You could also send the ECU out to get re-mapped.