First of all, I doubt seriously that it's a chrome plated feed ramp. If it is, the craytex usually polishes the chrome for a long time before it wears through. The bore is chrome lined but the feed ramp on my AR's and every one I've seen has been parkerized or otherwise finished.
Secondly, the craytex that I use is a polish and not a harsh abrasive. I know there are different grades, but the grade I use does not remove metal, but only polishes the surface.
Finally, with a light coat of synthetic oil you will never have to do anything but clean the ramp again. I suspect that the buildup is not carbon but merely finish if it is that difficult to get off.
Also understand that the chrome lining was to prevent damage to the chamber and the bore, not the feed ramp. This was also Vietnam and the problems were mainly a product of ill-equiped and trained soldiers. Assuming the feed ramp was chrome lined and you did polish it off, you would still end up with what virtually every other rifle on the market has, a non-chrome-plated surface. Oil it and don't worry about it. Heck, this isn't rocket science. You'd have to go through a case of craytex to remove any appreciable amount of metal. Have at it.