The upper thermostat housing is 3757230, x, gm. I gooled the number and it came back as outlet group number 1.153

The lower thermostat housing is 375723(x) x is either a 2 or 3. It was cut off by where on of the mounting hole where cut in so it could not be read. It does not look like a zero. There was not listing on google for the 3757232 or 3757233.

The round water hole on the lower thermostat housing is 2 1/4" water hole opening and where the brass insert or ring that the thermostat sets into the outer ring diameter is 2 17/32". I took it to the well known FLAPS and their gaskets with the 2 1/4" water hole opening is ok but the bolt holes are off. If you look at the 261 thermostat housing the bolt hole is not centered on the 2 1/4" opening because of the by pass port. On the ones from the FLAPS theirs are centered on the 2 1/4" opening.

http://i1291.photobucket.com/albums/b554/stovebolt56/20160130_184737_zpsqxwh7oma.jpg

http://i1291.photobucket.com/albums/b554/stovebolt56/20160130_184711_zpslz3zzcaj.jpg

http://i1291.photobucket.com/albums/b554/stovebolt56/20160130_185646_zpsknoa2mwk.jpg

http://i1291.photobucket.com/albums/b554/stovebolt56/20160130_185549_zpsyujkwatm.jpg

Last edited by Tiny_Jaime; 01/31/2016 4:02 AM.
"As I lay rubber down the street, I pray for traction I can keep, but if I spin and begin to slide, please dear God protect my sweet ride." -Amen

56 Chevy 3100