Can I put just the crankshaft from my 3.5hp briggs and stratton lawnmower into my b&s 3hp lawnmower?

I broke the bolt holding the blade onto my 3hp motor and it cannot be removed. I've tried drilling and removal tools and everything and it's just not coming out of there, so I wondered if I could just exchange cranks ONLY because the 3hp engine is exellent condition and the 3.5 hp engine is using a lot of oil.So are they identical sizes or not/ and if so then is all I need to buy is a 3hp gasket kit?