660 Thermostat Housing - Neck vs. Outer Lip

[Pacecar1969]

Is there an answer to why some 660 housings have the numbers on the lip and others have the part number on the neck?

[70 copo]

I looked at this issue a number of years ago and I wound up convinced that GM did a supplier change around mid 1968. Anyway the image below is correct for 1967 and you can see the contract supplier mark right on the casting on the lip along with the run number.

The later castings are up on the neck typically with a casting run number only as we are accustomed to seeing on the later cars, and the reproductions are also made off of this last version.

[rszmjt]

FWIW - IMO - Just about every known Original or Survivor Aluminum Intake car I have ever looked at in the last 50 years had the “660” housing with the casting numbers by the flange. I worked at a Corvette/Camaro Restoration shop for 20 years and this was noted. A lot of cast Iron Intake cars seem to have the housing with the “660” numbers on the neck.
My own original 06A 69 Z28 ( owned since 1974) has the housing with numbers by flange, & I have a untouched 6,000 mile 70 Z28 LTI motor & it is by the flange . Note that there are also small & large “660” numbers on the flange.
The diamond with the P inside I have also seen from Paragon Reproductions.
As noted by 70 COPO I think the housing with “660” on the neck seemed to come into production around 1968. Cast Intake cars usually have the housing painted orange, while aluminum Intake cars are natural .

Maybe others with known original housings can chime in on this post.

[Edgemontvillage]

Photos of my 1969 2B Norwood RS Z/28 during teardown. I'm confident based on tell-tale indicators that neither the manifold nor the thermostat housing had been off the car to that point. In fact the housing stud had fused to the aluminum manifold and destroyed the degraded threads on removal. The 660 housing has the part number embossed on the neck rather than the flange in this case.

https://live.staticflickr.com/65535/51026152132_f4081d7a46_c.jpg (https://flic.kr/p/2kK1niE)

https://live.staticflickr.com/65535/51026149967_6824614ca9_c.jpg (https://flic.kr/p/2kK1mEk)

[Mr.Nickey Nova]

My June built 69 Z has it along the lip, but don't know if it's original to the car. Maybe two different supplier thing, one along the lip and one on the housing.

[Edgemontvillage]

Jim B's 2A Norwood Z/28 survivor from its appearance at MCACN in November 2016 where it was Legends Certified. The engine compartment was nicely original with very few service replacements. Not the best angle for this photo however note the thermostat housing with the embossed part # on the neck.

https://live.staticflickr.com/65535/51027213257_4a7d724d0a_c.jpg (https://flic.kr/p/2kK6NJV)

https://live.staticflickr.com/65535/51027129821_bb8ae63543_c.jpg (https://flic.kr/p/2kK6nWn)[url=https://flic.kr/p/2kK6nWn]

[mhm1966]

My 03D 1969 Z/28 that is very original has the numbers on the neck.