On a 1999 502 MPI is the time cover stamped steel or is it a composite.

I believe a 99 is a Gen 6, that would be composite.
http://www.mortec.com/bbc.htm

marine engines fall weird as to gen's so if it's close take a look, the look visibly differnt or if not sure try the magnut trick...Rob

99 is a Gen VI which has a 6 bolt cast alloy cover not compatible with any others (they have 10 bolts).
Aftermarket Gen VI covers are hard to come by, I'm just going to srtip, polish and clear coat my factory one for looks!

Comp cams makes a gen 6 timing cover. I just bought from summit not long ago.
http://store.summitracing.com/partde...w=1&N=700+150+

Shaffirof has the best looking one that I have seen.