Nice truck and it looks like you are doing a great job with it. As an old Dodge fan I chuckle when I hear these called 1st gens. It's the 1st gen of the CTD but the last gen of these style trucks. The chassis is pretty much the same from '61-'93. Except the rear springs are shorter on the '61-'71s. Suspension is the same on the '71-'80 Powerwagons and '81-'93 Power Rams. Even some body panels will interchange. That's one of the great things about the older Dodges. 3 decades of parts interchangablity.
I have an '80 powerwagon and wish I got your fuel economy. I've got a 4spd and a mid '60s big block. Kinda thirsty.
KISS Principle = Keep It Simple Stupid.
Your best defense against Murphy's law!