I did spend some time the last two days looking at things - so your question was not being ignore
but the evidence is difficult to find (original engines with pictures of that area. One would expect that all engines at that engine plant (same one that did 428 CJs) would have the same practices on all engines built so I would guess we could open up the looking to 69 CJ's (lots more of those than 390 cars) but again not allot of un rebuilt or rattle canned intakes out there.
I did find the painting instructions for 70 windsor and clevelands and though not exactly the same thing there notes are as follows.
" Engine assembly must be painted all over to meet the performance of ESE-M210-B do not paint the following places:....
Carburetor mounting surface
Carburetor assembly
Spacer-carburetor to intake manifold mounting faces
........."
The spacer itself is not listed as a part to keep unpainted
There are 46 different items on that list. Looking at the list it can be concluded IMHO that the way the plant assured that certain items remained unpainted was to not install them until after painting while other items (supported by evidence on unrestored car)
Bottom line for me right this moment is that I can not offer a spacer with paint or overspray on it. I have seen that on 65-66 V8 motors in the past.