The hp increase again depends on a variety of things, but 3-5 hp is a range.
Removing 2 layers will put you on the higher hp end, and one layer less, but very effective. 93 octane is good. I personally would remove one gasket, because if you ever add pipes etc you cant have 2 layers out (yes its been done, but minimizes safety) You can see the tech area for a step by step, and you will not need to change jetting. cheapest hp around...
Good luck and enjoy your free hp. That sled will run well even with the relative low hp if tuned properly---primarily clutching.
John