"valve float" is really a misnomer. It's more like lifter jump. When the lifter leaves the lobe of the cam and there is clearance is what we usually call valve float. several issues can cause it, weak springs, weak pushrods, heavy lifter, too much rpm are the primary causes.

That all being said, you're running a heavy lifter at high rpms, not sure what pushrods you are using (are they thick wall ones?) and the valve springs on the Edelbrock head may not be up to controlling the valve train at the higher rpms you want to run. Hydraulic roller lifters generally call for a different spring spec than a similarly spec's hydraulic flat tappet cam (aggressive lobes tend to require stouter spring and aftermarket roller cams usually have more aggressive ramp profiles).

Good luck