Clearance issues at the fender cap are common on these trucks with larger tires. That is why I did this
https://67-72chevytrucks.com/vboard/...7&postcount=47
On my old K20 I just trimmed them with a sawzall.
Personally I would not use any type of block on the front. The zero rates are just a block bolted to the pack with the center pin. While they would not dislodge they still exaggerate axle wrap under power and braking. The front end will hop and under hard braking the truck will dart around. Yes, I tried them long ago. If used on the back it would increase your block size to 4.5/5" making wrap even worse there.
If you just do 6" front springs and an add-a-leaf in the back. You may need longer shocks so check that out. Could get away without the 2" drop pitman arm. Right turn will be limited at droop. Drivelines should be okay. I know this is not what you want to hear, maybe look into full kits? Have seen some still in the $600 range.