i have a kevco pan and windage tray. the Mopar book "How to build big inch small block mopars" says a gain of 40 hp by using a windage tray.
Read closely. You actually increase crank case pressure with the 3.58 stroke using the MoPar tray.
That is not the way to make power.
How much power you gain is going to be subject to a few variables......a deeper pan will eliminate much of the oil getting wrapped up in your rotating assembly. A tray will capture oil from the rotating assembly and keep it below the crank shaft in the sump where the pick up can do it's job.
But a scraper does this much more effectively than a tray when you are talking about removing excess oil from the spinning stuff.
Less windage = more h.p.
It should also help return the oil to the pan , but a scraper doesn't have the oil control capabilities of a tray or a good pan , where those can keep the oil in the sump.
The Kevco pans seem to be a really nice part for the money ..... a baffled pan with a built in scraper. The pan scrapers are typically not as efficient as ones that are specifically contoured to your crankshaft and rods. These are the Cadillacs of oil control. It is sort of free horse power........you pay once and until you kick the rods out of it , it will always do it's job.
40 h.p. is pretty optimistic. You would have to be improving on an absolute horse **** set up from the start. But I suspect that 15 would be a reasonable expectation.