If I remember correctly, you're using a standard MII setup.
There's been a number of discussions about it here and elsewhere. It seems the MII 4 cylinder are what most use for optimum comfort with an AD truck.
http://67-72chevytrucks.com/vboard/s...d.php?t=554035
http://67-72chevytrucks.com/vboard/s...d.php?t=438015
Some of it depends on where you're going to mount your tank, what engine, AC, etc... I see you're using an LS, which is lighter than a small block, but the 4L80 is pretty beefy.
I just recently finish the IFS install on my truck. Since I have a 3600 truck and I'm eventually going to add AC, I'm planning on using the 6 cylinder or even station wagon style springs for mine. I would rather have a slightly stiff ride than mushy handling.
Eaton Detroit has a good guide for MII springs. They have more selection than you know what to do with.
https://www.eatondetroitspring.com/o...-coil-springs/
As far as coilovers, can't help you there.