If you want a cheap and easy way to rivet the holder to the helm, it's just drilling 2 holes then using "speed rivets", which are small rivets that you attach with a little rivet gun. You can pick up the gun & some misc starter rivets for around $15.
I haven't really seen much of any plumes pre 15th-ish century, I think the torse and mantle is more appropriate to the earlier periods, if that's of any concern.
Alot of the illustrations in the 14th century manuscript, Guiron le Courtois c. 1370-1380, have knights with feathers as their crests, or at least part of.
This is about the clearest pictoral evidence for the use of plumes in the 14th century;
http://visualiseur.bnf.fr/ConsulterElementNum?O=IFN-08100550&E=JPEG&Deb=45&Fin=45&Param=C
Or here`s another in a manuscript with several Arthurian stories, c. 1380-1385
http://visualiseur.bnf.fr/ConsulterElementNum?O=IFN-08100550&E=JPEG&Deb=45&Fin=45&Param=C
G.
Oh wow, neat, I've never heard of that book. The second link opened to the same as the first but I saw the book with the crested helms. Thanks Sir Gerard!
