I think you're a little off on your dates. I don't think home sergers became widely available until the late 70s. I could be wrong. ManicMike knows a lot more about them than I do. But I think your 3 thread looks newer than mine and mine is from 1982. There are, and according to someone on WFI, always have been only around 3 factories that produce sergers. Juki, Babylock, The old Whites, Pfaffs, Brothers, and a few others I know came out of the same factory, they're pretty much all alike. I think mine did too.
It's a 1982 Consew Tuffylock model 94. IT. IS. A. BEAST. It's small but weighs a ton and will sew through anything. 3/4 thread. It's hard to thread but not that hard. What I don't like is if I want to only overlock the edge I'm supposed to remove one needle, which means re threading the whole thing. I just use all 4 threads and then pull out the chain stitch instead, lol. It came with the controller, the needle wrench and one extra needle. Found the manual on the Consew website. My thread stand was broken at some point and fixed by screwing a metal plate to hold it together but the metal is bent so two cones lean towards the others. A Seattle Goodwill find on Ebay for the princely sum of $12.00.
Cari