some of those "used to be" models are still being sold today
the 1/4 scale working visible V-8 is from the sixties, I had one, my cousin had another,,,,,his dad "helped" him and got just a touch of cement on the wrist pins,,,,I was one year older and didn't get any help, mine turned over but, the 3 in 1 oil I used for a lube during assembly all pooled in the clear oil pan sump,,,,my engine wound up demonstrating what an engine looks like inside just before an oil change, the oil yellowed and picked up dust, but, it did "run" as long as I fed it batteries,,,,,,,,,it is still sold today, it is Revell now, instead of Renwal, and has a hand crank to turn it, instead of a motor in the starter housing,,,,,,so, the batteries only have to run the spark-bulbs
there were 4 to 1 scale model Ants at one time,,,,,,and I think some of the Bird models were 4 to 1 or 2 to 1,,,,,I have this memory of a Huge Finch sitting on the window sill and keeping real birds away from that area at my Grandpa's house
When plastic injection molding was young, and just after the explosion of kits,,,,,,,there were hundreds of working toys that were made from the process,,,,,,,,we could get kits to build houses and skyscrapers, they had styrene panels for wall panels and the same plastic as "army men" for the dozen differently shaped girders