rGamblin.
Let me clarify what the basic rated load capacity of lift trucks means.
In the US you will see the basic rated capacity stated e.g. as 20,000 lbs at 24" load center or L.C. This capacity is based on a given configuration of the truck, e.g. 144" lift, two section (or stage) mast with basic carriage & forks and assumes that the load is lifted to the full vertical extension of the mast.. If you would select a three section mast and add a front end attachment like a jib crane or side shift. More than likely the net lifting capacity would be reduced to say 16,000 lbs at 24" load center.
The load center is measured from the face of the fork (the front of the vertical section of the fork where the load would rest against) to the center of gravity of the load in both the horizontal & vertical directions. When a manufacturer states the capacity rating at 24" load center they are referring to a homogeneous cube that measures 48" x 48" x 48". Most companies do it this way for sake of comparison & testing compliance to industry standards. When lift trucks get above 35,000 lbs. basic capacity you will often find that the capacity is stated at a 36" load center and at 48" (for container handling equipment).
In your business a fork mount jib boom is commonly used. The boom has various lift points to sling chains through to lift the various size of machinery. The lift truck manufacturer (through their authorized dealer) can provide you with the net lift capacity at each of these pick points.

The dimension from the center of the driving axle to the load center that lifter 01 provided you is used to determine the in-lb rating of the lift truck. This dimension includes the load center (e.g. 24") plus the truck's front overhang. I won't go into what this means - you only need to understand what the net lifting capacity is at various load centers with a given mast & attachment. You need to provide the supplier with things like how high you need to lift, fork length requirements, any attachment, maximum weight & size of loads you will be lifting.