I like the way Hung thinks. In fact, I like the way Hung thinks on a lot of things. A 1978 model with low-low airframe total time is very desireable. It could be the easiest 10,000 dollars you've ever made...
You're an honorable man to be concerned about keeping your word. However, if you explain everything to the seller of the '68, I don't see how he wouldn't understand your interest in the later model airplane. You were oogling over it before his, but the price was out of sight. That's not the case now. If you do talk to the seller of the 68 model and decide to give him some money when you walk away from his deal, give it to him in 100 dollar bills. That let's him know you're still an honorable man, and that you're taking care of things while looking down the road.
my opinion:
Objectively look at both planes without the human emotions/pride/feelings. Decide which one you'll wish you had in 3 years. Then go for it. Get a buying buddy for the objectiveness if you have to. But, don't let pride or your personal feelings get in the way of making a prudent decision. It's only 4000 more for the later model, but it'll be infinitely easier to sell later. Nearly a decade younger and oodles less time on the airframe...
I'm glad I'm not in your shoes, though. Good luck.
