My C10 is one of the better riding and believe it or not, easier to drive vehicles, that I own....all that I had to do was put in a computer controlled v8, an overdrive trans, new suspension, brakes, interior...oh and tub the floor 5" for legroom.
Despite my snark, each of those things was done to address some of the things you mentioned, just to a probably-unnecessary level.
The trailing arm rear allows for a truck that rides better than most trucks, even into many late models. A good shock and a reasonable tire profile should make for a pretty pedestrian ride down the road. After that, swaybars can really help even out some of the boatiness it sounds like you feel.
A 3spd auto or even a 700r4 can be put in without insane levels of cost or effort, and if that 4spd stick is bothering you, this might be a quality-of-life mod for you. Thankfully going manual->auto is MUCH easier than the other way around.
As the others mentioned, the sound deadening is another easy one that can be cost-controlled if you aren't hung up on certain brand names.
I think nostalgia had you in rose-colored shades on that 65 M-series though...no way that Ibeam front axle and leaf spring rear rode better than the chevy from the same year.