Any time parts in the valvetrain are changed, you need to check the geometrey.
I've seen quite a variaton between different brands of roller rockers. Base circle vary with the size and type of cam. Aftrmarket heads can change things drastically. Last Windsor I built(425ci) used Victor Jr heads and a solid roller- wound up with a 8.400 push rod-- which is probably 1/4 inch longer than stock.

Push rod size and wall thickness will depend on spring pressure and RPMs . 5/16 can be used in most mild and moderate builds.