Sorry, the micro switch was inside behind the diaphragm. There was a lot of corrosion inside so there may have been other stuff at some point.
The serial number I cant quite make out. I believe it is 9981506 or 99B1506 or 8981506 or 89B1506. Ive tried pencil rubbings but still cant make it out for sure. The other spot with the numbers I cant make out at all.
Yes, the bolts are stainless steel.