I made over 900 hp with the EZ heads on my 514 shortblock. That wasn't a very stable combination so I wouldn't recommend duplicating it but I'd think that a person could build a 850 hp combo that would go rounds using the EZ heads.

My heads were ported by Modern but I think they took them a little bit too far so you might want to dial it back a hair. I was running over 15:1 compression which was also a little too much so you might want to back that down to 13.5 or something like that.

Run the numbers and see if 850 hp is fast enough for you. If it is then you just need to get your heads ported and build the shortblock around them.