You don't really need to reinvent the wheel to get what you are after. The ride quality can be softened by doing just a few small things like shocks and removing a couple of leaf springs. If you your springs are worn beyond repair/rebuild, replacements can be found. Older springs will give a softer ride than say a new firm leaf pack. Rebuilding your current leaf packs and adding some sliders is not that difficult. A set of good gas shocks and Radial tires will go a long way towards improved ride quality. The addition of a front Anti Roll bar will help as well. Getting everything tight and correctly aligned up front is a major key to having a safe and drivable truck. These old trucks actually steer pretty easy once everything is adjusted properly.
As for gearing, the right combination is not that difficult to accomplish. Certainly the addition of an overdrive is a great idea, but only if you do your homework. While a lot of folks are opting for a T5 swap, in a 3/4 Ton truck that may not be your best choice depending on how you want to use the truck. With the correct tire size and the right rear gear your 3 speed or a 4 speed will do just fine. I say this after chasing a '48 3600 through the East Kentucky mountains this past fall. He had a solid 261 with a SM420 and 3.90- rear gear, running 65 MPH while pulling a 20ft camper (Ask PaPa Joe!).
I will say this, "Do your Homework". if the total package is what your after, a true daily driver that has the ability to work , it can be accomplished. Start with a goal in mind and plan toward that build, everything you do will add to the overall goal. Remember, make it safe, make it STOP, make it steer then make it go...
