new here help!!!

[c20let]

First of all hi everyone what i am planing on doing is buying a rolling chassis and putting a 250 ether a cr yz kx don't no what one yet now for the problems 1- what is the best frame to use to modify to fit the 250 or do i need to modify . 2- do i need to lengthening the back axle.I have seen just videos off the 250's in action and it looks like they don't modify the chassis to fit the 250 and dose any one on here have pics off a go kart with a 250 out off a scrambler in it i don't no the right name for the go kart i am wanting to use it is a track go cart like the racing ones thanks for your help