Need help with sickle mower parts!

I've acquired a project that my dad kind of started, it's a 7' IH sickle mower, a 27-v I think. It's complete but the wear parts are, well, worn and rusty and need replacing. I'm going to use it to cut rye and bermuda and some native type pasture. Was wondering what would be the best knives and guards to use. Dad had bought some new parts for it, but none have been put on. The old guards have serrated edges on the plates and the knives have serrated edges on the bevel. The new knives have the serrated edge on the bottom and the guards he came up with are in pairs but have no removeable plate. I'm not sure what is designed to be compatible with what or what would work best for my use.
What has been your experience?

We usually get two or three years out of the swather guards, much more convenient than changing ledger plates.