Seeing how this is a dream truck... and the possibility of having to do a frame swap. Get an estimate, but have a estimate of just a rolling chassis and an as it sits. Obviously, the rolling chassis will be cheaper but you will get a better product in the end as the tech can see the ripples...
So describe the harshness...
You didn't notice with the automatic but you do with the manual. I would verify all the items swapped when you did the NV4500 before blaming something that was there with both transmissions.
My thoughts are...
What is you gear ratio right now?
Does the axle match the front? Only ask because you have a 2WD in it, have you used 4WD since installing the axle?
How much money are you going to drop on the 2WD axle parts?
Depending on how much, why not upgrade to a 14 bolt semi-float...
You will need to choose. Clock or tach. Technically, you can't have both. There used to be a company that made Tach/fuel gauge in one that looked factory. So you could have the clock too.
IIRC, you can use an 80s camaro/firebird tach/fuel that fits the C/K trucks.
The lens with a clock...
Dash bezel is a 73-75, the gauges are; temp - 81 and up, oil press. (depending on if its mech. or elec.) 73-76 or 77-80, volts is 76-80, speedo is 73-74, blinkers are not arrows as a 73-75ish,
Big question is... What are you going to using the truck for? DD, dirt road driving, mild off-roading, boulder bouncer.
This is a key question you need to ask yourself. Budget and time are your next questions you have to deal with.
IMO, if you have a nice budget and agreeable time frame...