I have just finished looking at engine compartment pictures of 98, 1967 Mustangs, and 14, 1968 Mustangs. The 1967's included 56 from San Jose, 26 from Metuchen, and 16 from Dearborn. Samples included several "junkyard rust buckets", drivers, restored cars of various levels, and several low mileage originals. The Build Dates are not known of any except my 67. I did not separate the 68's by Plant. I looked at the Radiator Supports of all of the 112 cars in the sample, not just the ones with Factory A/C.
Factory A/C appeared on the following :
San Jose - 20
Dearborn - 3
Metuchen - 8
1968's - 8
Several interesting observations were made :
1) All 67's sampled that had the blow-molded Windshield Washer Reservoir (From 3/01/67), had a full knockout on the Radiator Support instead of the slits and dimples. Since the only known Build Date of those sampled is my 67, I can say that, for Dearborn, the change to the full knockout occurred after January 31 and by March 1, 1967.
2) "Throwing a wrench" into making a statement that all cars built after 3/01/67 had the knockout is that one of the 1968's had the slits and dimples ??
3) On all of the "slit/dimple" cutouts that could be seen (a few were obscured due to having the correct foam/sponge gasket around the condenser tubes and pushed to the opening), the circular portion of the cutouts appeared to have been made with a hole saw of slightly larger diameter than the distance between slits. In addition, all of the circular portions of the cutouts appear to have a square edge (as opposed to a slightly rounded edge usually seen when punch tools are used for such holes), and most, if not all, exhibited burrs around the circular portions.
4} Factory air Conditioned cars that exhibited a "clean" oval opening appear to be the result of them having the knockout as opposed to the slits and dimples.
5) On one 289 from the SJ Plant, it was obvious that the Factory Air must have been added at sometime after the Dealer received the car (could have been in 1967 or 2017), as the cutout for the condenser tubes was a jagged square cutout, wider than the distance between the slits, and less than half as tall as the correct opening.
6) Of the 39 samples observed with Factory A/C, 5 or 6 were 390's. On the ones that did not have the foam gasket covering the opening (4 as I remember), all had additional cutouts extending to the inboard side of the "normal" cutout. Whether this was typical for the 390 applications, or the result of Service Parts or aftermarket parts not being identical to the Factory parts, is anyone's guess..
SUMMARY
Based on the above observations, which, granted, is a small sample, I venture to make the following conclusions :
1) At sometime prior to 03//01/67, the Radiator Support was changed to include a knockout for the A/C Condenser tubes instead of two slits and two dimples. This may, or may not be the same change that is noted as having taken place in March of 1968 where the Service Part Number changed from C7ZZ-16138-A to C7ZZ-16138-B (although that seems like a long time for a Plant change to be implemented on Service Parts).
2) On cars built with the Radiator Supports with slits and dimples, it appears that the Factory used a hole saw in the dimples to result in the complete oval opening. While an electricians chassis punch may leave a cleaner opening, it doesn't appear that it was what was used.
3) As mentioned previously in this thread, a quality hole saw, with cutting lubricant and a slow and steady pace will result in excellent hole cutouts.
4) Since all of the samples in which a hole saw appears to have been used (those with the slits and dimples), the resulting hole appears to be of a larger diameter than the distance between the slits, a hole saw of 1/16" diameter smaller bay result in a much more uniform looking opening and eliminate a "keyhole" type effect. Although, this then would not really emulate what apparently was done at the Plants.
5) As the condenser is bolted to the Radiator Support, and the condenser tubes are ridged steel tubes, there is no concern about the tubes rubbing on the cutout opening, unless, of course, the condenser becomes extremely loose in its attachment to the Radiator Support.
All of the above are my opinions based on what I observed.
Hope this "exercise" helps ; if nothing else, it might open up itself to more questions and investigation.
Bob
