It was considered complex when I learned to fly it in 1976. You are right, rules since changed.
IIRC, it was considered "high performance" back around then, and that should have been the wording in a pre-1997 endorsement for a 182, but so was a 180HP Mooney. The original additional training endorsement rule lumped all airplanes over 200HP and all airplanes we now call "complex" into one "high performance" set. However, I don't think that HP stuff started until 1978, so I don't think you'll have a HP endorsement from 1976 -- you'd be grandfathered based on your pre-78 182 time, rather than endorsed for HP. Could be wrong, but I can't dig up the FAR's from before 1978.
That was great until they reversed course in 1997 and created the then-new "complex" definition with a separate endorsement requirement. Unfortunately, they kept the "high performance" term for those aircraft which were not complex but had an engine over 200HP, and even kept the paragraph number the same (61.31(f)). The result is people who got a "high performance" endorsement in a plane with no engine over 200HP before 8/4/97 and never acted as PIC in a plane with an engine over 200HP before 8/4/97 have an endorsement which is not valid for the current definition of "high performance" airplanes.
I've bumped into a few people like that, including one IR trainee in a 300HP Piper Lance in about 2007 who had been flying that plane for about five years illegally because the only endorsement he had was a "high performance" endorsement he'd gotten in the 90's in the Arrow he'd previously owned, and he had not flown anything over 200HP before he bought the Lance. Had he flown a 182 or the like between his original HP endorsement in the Arrow and 8/4/97, he'd have been grandfathered for HP under the new definition, but he hadn't, so he was not legal to fly a plane with an engine over 200HP after 8/4/97. It was easy enough to give him the proper endorsement during IR training, but he had five years of illegal flying documented in his logbook if they FAA ever cared to bother with it.
Likewise, if someone had obtained a HP endorsement in a 182 in 1995, that would have been valid in an Arrow from hen until that reg change. If they logged even 0.1 PIC time in an Arrow between getting that endorsement and 8/4/97, the logged PIC time would have grandfathered them for complex starting 8/4/97. If not, they would need a complex endorsement before acting as PIC in a complex airplane even though they'd have been legal to do so up until 8/4/987.
So, when I'm giving anyone training in anything now considered either HP and/or complex, I go back and confirm the source of their HP and/or privileges -- post-97 endorsement, pre-97 endorsement, or grandfathering. If it ain't right, I make sure I put the necessary endorsement in their log before they go to the examiner lest they get sent home in ignominy and the examiner tell the FSDO I screwed up by sending someone to the practical test in a plane they weren't legal to fly.
Silly reg stuff...