I wonder how many of the "accurate" models of yore were sized to fit their box(?)
I've been doing some repacking of old builds into a particular sized box and am amazed that a Jo-Han '69 DeVille and an AMT '66 Wildcat each just fit into this box.The real Caddy was longer that the real Buick.
Most are unaware (and were back in the day), that automakers (GM in particular) were rather adamant that all promotional model cars fit in exactly the same box (or as in the case of the new-for-1962 compact cars, two standard sized boxes). That lead to some rather creative "dimensioning" on JoHan's part for their 59-62 Cadillacs: Overall, their bodies are only slightly longer than a 1/25 scale Chevy Impala, but yet are a tad narrower. Their front clips and trunk area's are shorter than they should be, while the "greenhouses" are very close to the correct length front-to-back, the entire body shells are a good 1/8" too narrow (3" in 1/25 scale). From 1963 all the way out to the last JoHan promotional and kit Cadillacs (their last one was the 1979 Fleetwood Coupe de Ville) are all seriously undersized, no larger than an early-mid 1970's Impala, as you noted.
JoHan's Studebaker Lark promos (1960, 1961 and 1962--the 62's were morphed into 3in1 model kits) are all oversized, approximately 1:22.5 scale, which makes them tower over most any other 1/25 scale model car kit.
AMT/SMP comes in for some criticism as well, at least from me: The SMP 1959-60 Chevrolet Impala convertible kits all have a terribly inaccurate windshield frame, that having a pronounced upward, curved "arch" to the top of the windshield frame, and the '60 Chevy grille only barely resembles the real car's--and does not begin to fit the kit body shell at all correctly or cleanly. Their 1960 El Camino and '60 Impala Nomad 4dr station wagon bodies have roof lines that are the lower hardtop/convertible height, when the real cars' rooflines were a good 2-3" taller, with a more vertical windshield. In fact, the only accurately done Chevy bodyshell from that era of Chevy is on the '59 El Camino (which started out as a much more highly detailed "Trophy Series" kit. The SMP 59-61 Corvette kits (as well as the AMT '62 Corvette) have a front end that is almost as blunt as a brick--and the lower pan is far to square--to the point it almost suggests a chipmunk with cheeks full of unchewed nuts. The chrome "wheel covers" on the SMP '59 Impala HT kit are not wheel covers at all--SMP tooled up the standard equipment "dog dish" hubcap on a steelie, as opposed to the very stylish and popular Impala full wheel cover.
AMT's almost iconic '61 Pontiac Bonneville kit bodies are not symmetrical--that bold, raised character shape down the sides closely matches the real car on the right side of the body, but the left side? Ewwww! It's not even done straightly!. Their '65 Bonneville HT kit has a correct shape to the right rear quarter window opening, while the left side is way off--too arched, the C-post too vertical as well.
AMT's '32 Ford kits? Lots of inaccuraces there, roadster and coupe bodies whose shapes only resemble the real thing (Revell has gotten their 21st Century kits of the Deuce much, MUCH more accurate. The AMT '32 Ford Phaeton and Tudor sedan bodies are considerably too narrow behind the B-post, and the Tudor sedan body is far too rounded at the roof behind the B-post as well. While AMT's 40 Ford coupe and sedan kits are actually pretty accurate, their '40 Ford sedan delivery body is considerably too narrow aft of the B-post, and much too slab-sided--all this happened apparently to allow the use of the coupe/sedan fender/running board unit.
Now, lest anyone think I'm just dissing those old models and the people who created them, I'm not, really. They were the product of companies just learning the fine art of creating decent plastic model kits--in the case of their "annual series" customizing kits, they were handicapped by having to deal with only such information as the styling departments of the automakers were willing to let out to them, and only minimal measurements at that. The pattern-makers were still in a learning curve I suspect--most of them, while highly skilled, were more than likely recruits out of other industries and had to transfer their basic hand skills from creating tooling for say, consumer goods to miniaturizing real cars into model kit tooling. There were only limited factory drawings of those body shells, most real car body shapes were transferred from clay mockups to steel tooling without benefit of drawings or certainly 3D scans (that technology in the late 50's was a good half century out into the future.
But, since the premise of this thread is accuracy yesterday VS today, in general, model car kits of those days of yore weren't necessarily better than what we see today--albeit they were masterpieces of the designer's and toolmaker's art.