Valve covers for trickflow heads

The text you copied above is specific to the fabricated valve covers sold through 440source. Factory heads were not drilled straight for some reason, and the text is indicating 440source valve covers are set up to match that angle of the factory heads. That is why using them on an aftermarket head with straight or perpendicular holes won't work. It does not apply to the cast Mopar valve covers being used on aftermarket heads because these do not use the really long bolts. Mopar cast valve covers should work on Trick Flow heads.

However, the gasket flange area of the Mopar valve covers are rough cast and are set up to use a cork or rubberized cork stock style valve cover gasket. If the gasket does not match the cover or head well it will likely leak, as you are running in to. They often crack if overtightened too, so check them very carefully.

If you do want to replace the covers, Trick Flow TFS-61611802 is a cast cover that is machined flat, so it works better with all types of gaskets on any head with a machined flat valve cover rail like your Trick Flow heads.