1969 Z/28 Camaro "472" Intake Manifold Expansion Plug

[Edgemontvillage]

I'm cross posting from the CRG site as I'm not getting traction on this question. The original, steel intake expansion plug from my 472 intake manifold was lost. I sent the intake to a well known restoration shop for re-skinning and was surprised to see the replacement plug they used was stamped with manufacturers' marks. The original, factory installed 1 1/4" plugs had no marks so what I now have is incorrect. I have been trying to source a correct replacement steel plug and have ordered them from eBay sellers as well as Heartbeat City. Contrary to item photos they all arrive with some form of manufacturers' stamping marks. I have even tried to grind out the stamp however the result is not suitable for a quality restoration. The original 302 from my Z/28 which is being rebuilt needed a set of replacement frost plugs which I was able to source from a Corvette restoration parts supplier with no manufacturers' stamping marks however I've been unable to locate a correct replacement intake expansion plug. Anyone have a confirmed source for unstamped, 1 1/4" steel intake expansion plugs?

472 Intake with an incorrect replacement steel expansion plug showing stamped manufacturers' marks highlighted (source: eBay)