Ford

Hello guys, I'm a new guy to bikes so please take it easy on me, long story short...Yamaha says my crank shaft is broken and to replace it with Labor and everything...it's gonna coast me the price of a secondhand 400 what I have the option to do now is to put a dragster 650 engine in which is gonna be the cheapest and most convenient solution to me. Now my question is will the 650 engine fit on the 400 frame? coz as far as I know everything else is the same. Please advise guys thanks allot - Ford