"You have to remember that those were the "Throw away Home Depot/Lowes/TSC mowers" of their day, so not many of them have survived."
I have to disagree!
Those riders were well built and pretty reliable. ...We sold them from our dealership.
They were intended for smaller suburban lawns and were limited to mowing and pulling a small cart. ...People that needed snow removal, a tiller, or had a large lawn would opt for a tractor instead.
Even if the mower lasted for 20-30 years of use (doubtful), mowers were not considered collectible, or worth the expense to restore them, so most were scrapped many years ago.
Don"t forget - 1967 was 47 years ago!