rate this stuff for add some horses on a 318

Not sure what compression ratio you're looking for. The 399's (like the flat top 167's) have a higher compression height than stock (1.81"), so the pistons won't be down in the holes much if any. If you have 64 cc chambers and the pistons are close to the deck (as they should be, even if the stock pistons were .1" down) you could easily see a compression ratio at or above 11:1 with that combo, which could mean race gas only with the stock cast iron heads.

And I would check valve to piston clearance with the domes. Shouldn't be an issue but I would check it.

525cfm will be on the small side for that engine, especially with that compression ratio. I'd suggest at least 600cfm, maybe 650.