The United Airlines aircraft shown when the Slades leave for Guatemala is a 1952 Convair CV-340-31, registration N73109. It flew with United until 1969, then with several smaller airlines until 1995 when it was withdrawn from service and stored. It's registration expired in 2012.
(56:15 on DVD) Hoyt hears Susan take off on her horse because she's upset, then he sees her galloping away. He runs to get a horse to follow...and conveniently comes out of the stable immediately with a horse already saddled? If he'd had to saddle a horse, as should have happened, he never would have caught her, but no one leaves a horse saddled all the time for such "convenience".