Thanks for the photos of the manual!
Nesco reintroduced their oval roasters in the 70s as slow cookers. Your Roaster booklet makes no mention of that, does not mention putting the porcelain inset pan in the dishwasher and the address on the back has Zone 16, so I think you have a real oldie there. They last forever and keep cooking. I have an oval one and a round one that are old.
When Rich's opened their cooking school in the early-mid 70s with Nathalie Dupree at the helm, those of us in the housewares departments in all of the stores were her guinea pigs; one store each day. She had chosen equipment from the store, but did not have a great grasp on small electrics. She had the people who worked in the small electrics departments make pate aux choux in the just introduced Cuisinart food processor, but her staff filled an orange Nesco oval roaster with oil in which the students were to deep fry the little pastries. Well the thermostat was set at 375 and the signal light went out, but the little balls of dough did not even make bubbles. I saw what had happened, explained it to her and went out on the floor and found a real deep fryer with the guts to do the job, maybe a rectangular Nesco FryRyte. We cleaned the packing dust from it, filled it with the hot oil, carefully, and fried the hell out of some dough. Of course we could have done the frying in a pan on the Sensi Temp Burner, but the purpose of the class was to use small electrics. Each cooking station had an absolutely beautiful 1974 GE TOL 30" Range J39001WH. I stood in front of that range and whispered a prayer that I would have one one day. I have had two thanks to John: a harvest one that was coated in grease and had really been abused and then the white one that is in my living room now, rotated from the kitchen to make room for the Amana ME Range, so full of Corning Ware that it might fall through the floor one day.