Cast/rigid covers are best for sealing... but they are heavy... I currently use them (Edlebrock)... but have considered getting some light-weight stamped aluminum covers... I think Morosso has offered them... probably saves maybe 2-3-4 pounds off the front-end... but would then absolutely check for flatness, especially at the bolt holes.. and probably use some bolt-load spreading washers at each bolt hole to prevent metal distortion.... and good quality cork-rubber gaskets (Fel-Pro's Cork-Lam... having metal middle shim with top/bottom cork-rubber... I like those the best... keeps their shape and lasts a long time!)... good for conformability.