.

I think I want to change my estimate on age to 1966. 

The indented corner 'french' graphics was used on other GE appliaces, specifically the built-in ovens from about 1964.  But this is Avocado, which correct me if I'm wrong, started in about 66.

It's a miracle this near BOL item lasted.  It must not have had much useage.  

What scares me most: the rust spot in the sump.

It's an SD-300B which means it IS from 1966 but it is NOT a BOL; it's a respectable MOL. Can't tell if it has a Power Shower, but it has the old-fashioned mechanical Rinse dispenser, which seemed to work and this sample has the wrong silverware basket. You can tell because the rack has two prongs that were for the older basket which would have been white. Interesting to note in the catalog that the rating of the heater coil was bumped back up to 700 watts. If you collect GE dishwashers, this would be worth considering because of the distinctive design of the control panel which didn't carry over. The rust in the sump is worrisome, but I cured that on one of my GE's with a small square of aluminum duct tape which is still holding. IMHO GE dishwashers took a long-lived dive when they switched from the Pull-Outs to the Front Loaders; I think they were shooting for huge sales which they got. I don't think they became respectable again until the late '90's.