Hi ,I have a word of advice ride a 250 and see if it is what you like because I have built a few of these things and what works for one guy may not work for you and all the conversions work differently. I am 6 foot 5 and the first generation CRF 450 fit me way better than the 2005 CRF 450 but I did not like how stiff the 1st gen 450 was UP FRONT other than that for me a bigger chasses handles better but I am in sand and like a 500 that works in fast conditions and is stable up front.
I here if you are big and like faSTER RIDING A 1ST GEN kx 450 IS THE TICKET.this came from MPS who has built alot of bikes.