The reason the AMT '70 Mach 1 appears so wonky is the promo contract was canceled, and they had to rely on spy shots to get the scoopless quarters looking right. The whole business was in upheaval at the time, as you implied. The 1:1 business was in a flat spot as the guns and butter economy began to stall out, and the Vietnam War was at its peak.
I believe they still had the business in '71-2, but don't recall any promos from AMT after that... maybe Pinto or Mustang II?
AMT was the broken watch that was correct twice per day - they were backside over teakettle in the production of 1/25 scale big-rig trucks, which I recall being very popular, and guessing at the economics of the business, quite profitable. The addition adjacent to the original building on E. Maple Rd. undertaken in the 70's was to accommodate the increase in production. Countdown kits were basically free money - and highly subscribed. The fact they are so easy to find even today is a testament to their popularity.
Some poor decisions would follow - a fair amount of money invested in subjects that went nowhere, and subjects ignored that could have been big business.
Ultimately, they were caught in the swoon between the end of the first wave of baby boomers (b. 1946 - 1957) and the crest of the second (1958-1964 ) which would come later, and be far more influenced by popular culture / licensed products (Dukes of Hazzard, Smokey, etc. )