11 rwhp isn't bad for just a rocker swap- safe to say that's at least 15 hp at the crank. But IMO if you're looking to even get close to newly built 455 with fresh 6x's, let alone any iron heads that are ported and bumping the SCR up to 9-9.5:1, you're gonna need more than rockers to make any noticeable power improvement.
A 4-bolt 455 HO block is an excellent foundation for a high performance build- I've seen some builds where the stock round ports were ported, and along with the right roller or solid cam, power outputs in the neighborhood of 500 hp were achieved. But if you're a stock purist and porting your stock heads are not an option, get some Edelbrock aluminum heads, a PPR TC-01 HF cam, and you'll be at 500+ hp. It also goes without saying that you should be upgrading to forged pistons and rods if you're at this power level.
Geno
