Hot Rods flathead exhaust valves

I am dis***embling the 53 Merc flathead I bought a few weeks back and running across some difficulties finding information about some of the parts I'm finding. Today's puzzle was the exhaust valves - they are marked RMC X3284 near the tip, they're 1.630" dia. (yes, this engine has 1 -5/8" intake and exhaust) and appear to be stainless. I tried looking up the part # but couldn't find anything online. Does anybody have an idea what these were originally intended for? Thanks to you flathead gurus (and this engine), I'm getting a little education on the flathead. As an aside, my Dad left me a KD 245 lifter tool for flatheads, with his tools when he p***ed away several years ago, so I guess he's helping me now.

 

I run Chevrolet exhaust valves in mine, may be what you have.