There is for the full size. If you like I can check to see if I can find one for the Beaumont/Chevelle as well. 

5738462 group 2.559 is the part for 65-66 Canadian Pontiac and full size Chev. This has to be one of the most elusive part numbers ever. The only way I was able to even find it was the 1966 Canadian Pontiac assembly manual has it in an illustration. Using that part number I went in to the numerical index in the parts book and was able to find it in a Canadian Pontiac parts book dated June 1966. The next issue I have is November 1969 and by then it has completely disappeared from the book, as if it never existed. The other place I found it was in a 1965 Canadian full size Chevrolet parts book dated Feb 1965. 

Now, for the Beaumont and Canadian Chevelle part number, I can't find a thing. My oldest Beaumont book is 1969 and it has nothing listed. It's a long shot but does anyone here have a Canadian parts book for Chevelle maybe dated older than 1969? Or a Beaumont parts book dated older than 1969? If so, can you please check for a "Retainer, wiring harness to rad support" in group 2.559?

66 Beau wrote:

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My Beaumont Parts Book No. 692A, 1964-69 Beaumont, Group 2.559 shows this:

and,

 

-- Edited by 66 Beau on Friday 2nd of December 2022 02:43:26 PM

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 Ok, so that's the same as the Beaumont book I have and it doesn't even mention such a part exists. Hopefully someone has an older book. An older Canadian Chevelle book would work too but it has to be GM of Canada, not the US book. 

Could something like this, say in the 3/4"x 48" size be a reasonable fill in until one is reproduced or you find a nice one?

https://www.cabletiesandmore.ca/black-cable-raceway

This looks like the ticket to me. Canadian supplier, includes both the one over the radiator and the one across the firewall...

https://www.classicchevy.ca/oer-1967-72-chevrolet-gmc-wiring-harness-retainer-plastic-wiring-gutter-firewall

Yes, it's for a pickup, but pretty sure it'd work. Might need to be trimmed to shorten it for a Beaumont or Acadian, but should be very close for a full size car.

I think this website provides a better picture of what the part looks like...

https://www.lmctruck.com/1967-72-chevy-gmc/cb-1967-72-plastic-wiring-gutters

Ya, the truck one for across the rad is very similar, probably the closest of all,   but it is still very different profile from the original canadian ones

those samples mark posted are interesting,  chinese variants, if only they could make it in the proper profile,  maybe we should start getting it reproduced?  i wonder where a guy would start?  what company could manufacture such a part?

I was confirming the style used for the Chevelles & Beaumonts for '67. I figured these are all 1st gen A-bodies.  When I check under the hood, the original stuff in my application is more like handlebar tape or even cloth elbow wrap. In this application I believe it is cloth tape. It is original and a little gummy or oily after so many decades. It is wrapped around the whole forward harness, across the rad support hidden & clipped within the rad support channel. That is apparently what they did on the A-bodies in 67. The 65-66 you are saying has a conduit that they run the forward wire through across to the battery side. Hmmm. I wonder if Home Depot might have something, or maybe an arts & crafts store. It might look right but may not meet certain specs in terms of fire retardancy or resiliency with respect to oil. Maybe ribbed heater hose, sliced lengthwise. That would be too thick though. A thinner version would seem like the ticket. What many would do when faced with this is simply run the wire through flexible PVC pipe as they did on 1970s-onward in GMs. 

I hear you though, the correct details can make a car stand out.

Red herrings:

1. The U.S. Chevelle AIM for '67 gives tape a part # of 3724851

2. I still have the factory firewall gutter on my car. They often would split over time. Reproductions are available so no big deal.

Yes, he's asked me for them as well. I suspect he would be interested in helping fund a reproduction of this piece. 

The only economical way would be an extrusion, and that would be easy.. But it would be extremely difficult to get that pebble grain...wait... this must be a molded part!