The one slant I fooled with had a .530" Isky solid in it, full length headers, 4 bbl, much of the same stuff as yours. I did run double valve springs, which I'm not sure is necessary with the small, light valves in a slant, but I ran a 750 cfm. carb. I pinged it off 7K a bunch of times. I don't know how high it would rev before it would skip, I never had it happen. Can you borrow a bigger carb to try? Everyone thought I was nuts running that big of a carb, but it ran really well.