Just in from Tim
"We sell the cross-ram tops for $300 pair. Hp increases depends on total output of the engine. A 500hp engine will see little increase, and one of our NSS 1000hp 604’s will see more than 50hp, as their air flow requirements are quite different. The stock covers tend to warp and leak quite a bit as well, along with being ugly"

Over to you man, call or email Tim he is great to deal with.