I used the Comp 1.5 roller rockers with their polylocks on 6X-4 heads with the factory rocker studs and a Comp XE276HR cam. My cast aluminum M/T valve covers were about 1/8" taller than the factory stamped metal covers and would not clear the polylocks, even with the 1/4" thick Butler gasket. I had to add Butler's spacer and another gasket for enough clearance.
Then the A/C compressor didn't clear the valve cover and I had to convert to a CVF serpentine belt drive. I wish I had known about the short polylocks.
Those rockers wound up costing over $2000.
