Yes, as Peter confirms below, this is a Heuer case - what I call the second economy series in my economy table, encompassing 7721/3/5, 73321/3/5 and 73623 that I have found. Regarding the case material discussion, the indicator numeral applies - watches ending -1 are plated base metal, whereas those ending -3 are stainless steel. Not sure why they felt the need to create a cost hierarchy within the economy models, but it's probably just about reaching the widest market for the watches. The third economy series adopted steel cases all round.

There are quite possibly 73621 and 73625 models too, but Vj 7736-powered models aren't in the catalogues and the one we have seen was in steel. If anyone has one of those two, I'd be interested in seeing photos.