Your getting more vacuum and that increases intake velsoity on the throttle transistion to WOT. At WOT your not creating more vacuum but having more accuracy in your valve train is going to help out alot at WOT. The engine is not working against it's self and unbalanced cylinders combustion wise. My guess is that if it running cooler things have increased fuel wise on the intake side and it's not running lean. Lean can mean power but to much creates heat and zapps power. I think that with everything for lack of better word more accurately tuned in the valve train your seeing you gains. I think the big block can handle the 1.8 ratio rockers and they would be a good choice.....I have to keep reminding myself you have to pass smog though. Your still on the stock cam correct? Have any of the gains your noticing now givin you an increase your happy with....comments above I think confirm your happy but do you want more? Would you have been happy and expect to get what you have done to this point with the intake, cam and heads you were thinking about in the beginning? Or where your expectations of the heads, cam and intake much greater than what you have gotten now? Be honest with your expectations and what you have accomplished. If you want a little more the 1.8's might be a good choice. They are cheap way of doing a "little" cam increase with out changing out your cam. Just the roller tip rockers them selves will give that "little" extra, the canted valves react to a roller rocker or roller tip very well by freeing up friction from the valve train. Be prepared they are noisy and can sound some what loose is the only way to describe them....it's a more solid noise and not the clack of loose rocker. I personally would do the 1.8's smog be dammed and change them out if you have issues with passing the smog check for the stock rockers every 2 years.