Tuning a 850 10v

I own a Volvo 850 2,5 10v from 1995 but i think it is a little slow. My thought was that i could change the cylinder head from a 10 valve to a 20 valve and this was get 170 hp out of it. is this tuning even possible ? are the 10v and 20v engines completely the same except this cylinder head?

I hope you guys can help.
 
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