That 1975-era Wards canister is a model SP-316 but has the SP-311 power head. The seller says it was made by Rexair, but in reality it was Eureka who made it (both the vacuum and the power nozzle). He apparently doesn't know that Eureka had sold power nozzles to Rainbow-Rexair.
And speaking of that, my maternal grandparents have a pre-1979 Rainbow D2 (s/n 3738819) whose power nozzle once belonged to a Wards SP-311 canister, because the powerhead, modified for a 3-wire receptacle by some Rainbow dealer at the request of the owners who had it before my grandparents, has a nameplate that suggests why it wasn't a Rainbow nozzle at first.
However, in the early 1980s, some of the 1975-80 Rainbow D2(A) and D3A models were later modified to have the older-style 2-wire receptacles for the power nozzles (like the original 1974 models).
~Ben
