The only ones I've ever seen were not in Olds but Fords, and some Chebbies. And, they were chrome. I'm not sure why one repoped in fibergl*** would be any good. I see them for sale, from time to time; and unless you're in a hurry, find a nice old one and replate it. Yeah, I know, old ones in good shape are hard to find. I've been looking for one myself. When I do see them for sale, I don't have the money; and when I have the money....you know how that goes. Don't give up looking. Fibergl*** is like giving up on being part of a tradition, which is suffering while you waste time looking for that absolutely perfect part you need and can't live without; when you could be wasting time watching TV, movies, or on the Net. Welcome to Traditional, sometimes it hurts so bad it feels good, as the song reminds us.
I've seen older aftermarket alloy repops and parts turn up now and again on E-Bay, bottom plate and the bars themselves. I can tell you that the OEM cast grill weighs a TON. I had my 46 Olds grill rechromed before it was re***embled, covered with grease and wrapped in towel to preserve until ready. Chrome isn't cheap either. Pitting is a big issue as well, you need to find a good chromer that can triple plate it if you go down that road.