Gen VI will have a timing cover that is composite, with a indicator molded in the timing cover, the Gen V's will have the metal timing cover and the timing indicator that shows the 0 4 6 8 timing #'s on the indicator. (Looks like a Saw Tooth)
Gen V's will require a specific head gasket for the Gen V heads. Gen V's will not work with Gen IV heads.
The water passages on Gen VI were slightly modified to accommodate a GenIV head.
So the Gen VI gaskets should work on either the GenIV's or VI's.
The only GenIV 502's that were made were done by mercruiser using Bowtie blocks.
If you take a pic of your timing cover I can tell you right away what you have.