If you're worried about clearances with RR's, you can probly get away with reusing the stockers... I did on my setup w/Comp P.M. RR's and TW heads, just gotta take out the oil fill baffle on the passenger side cover
I think he means, will if fit under the intake manifold. I have seen tall valve covers not fit under a trickflow intake, and the owner had to use a phenolic spacer to move the upper up away from the valve covers.
I had a little bit of a clearance problem with throttle linkage when I put Ford motorsport valve covers on. I added a 3/8" phenolic spacer to gain enough space.
The valve cover surface of the TW heads is taller actually raised to help with RR clearance (.300" if I remember).
Since there are a ton of possible combinations that you could use it may be a good idea to measure things out before you buy something. Or just buy it and see if it fits.