Here's what I determined for 1973-1987 and 1967-1972 Chevrolet C/10 pickups:
1973-1987:
FRONT GR2 344068 Shock Absorber 2 RWD
REAR GR2 344072 Shock Absorber 2 RWD
FRONT GAS-A-JUST KG5409 Shock Absorber 2 RWD
REAR GAS-A-JUST KG5415 Shock Absorber 2 RWD
FRONT MONOMAX 565032 Shock Absorber 2 RWD
REAR MONOMAX 565036 Shock Absorber 2 RWD
1967-1972:
FRONT GR2 344068 Shock Absorber 2 w/ Coil Spring RWD
FRONT GAS-A-JUST KG5409 Shock Absorber 2 w/ Coil Spring RWD
REAR GAS-A-JUST KG5416 Shock Absorber 2 w/ Coil Spring RWD
FRONT MONOMAX 565032 Shock Absorber 2 w/ Coil Spring RWD
FRONT GR2 344068 Shock Absorber 2 w/ Leaf Spring RWD
REAR GR2 344085 Shock Absorber 2 w/ Leaf Spring RWD
FRONT GAS-A-JUST KG5409 Shock Absorber 2 w/ Leaf Spring RWD
REAR GAS-A-JUST KG5419 Shock Absorber 2 w/ Leaf Spring RWD
FRONT MONOMAX 565032 Shock Absorber 2 w/ Leaf Spring RWD
REAR MONOMAX 565037 Shock Absorber 2 w/ Leaf Spring RWD
For the '73-'87 trucks it mainly depends on the type of KYB shock you want to purchase. As for the '67-'72 trucks it depends on the type of KYB shock, but also the type of rear suspension. It looks like there isn't a difference on the height, or lack there of, of your suspension travel. Low and slow...
KYB Shock Difference:
KYB GR-2® / Excel-G®
twin-tube shocks, struts, and cartridges
Purpose: Restores a vehicle’s originally designed handling and control
Calibrated to compensate for worn suspensions
Components and valving are designed specifically for each application
The best choice to restore OE performance and normal driving conditions
Built with quality that matches or exceeds OE
Coverage for domestic and import cars, trucks, vans, minivans, and SUVs
KYB Gas-a-Just®monotube shock absorbers
Purpose: Significantly increases vehicle stability, handling, and control over twin-tube designs.
Gas-a-Just is the replacement for an OE monotube shock
Ideal as an upgrade from an OE twin-tube
The more responsive monotube design automatically adjusts to driving conditions
Applications for cars, trucks, vans, and SUVs
KYB MonoMax®heavy duty monotube shock absorbers
Purpose: Maximum control for trucks and SUVs – stronger, more durable truck shock
The right choice for hauling, towing, or plowing
The best performer on harsh road conditions
Perfect for diesel trucks
Applications for light trucks, vans, and SUVs, including some lifted and lowered vehicles
I hope this helps guys...