ANYTHING past the boom tip is EXTRA weight on the existing boom and support structure, the "16' jib" is considered weight, this x the weight on the jib is what IS on the boom tip, this weight CAN add up quick. The load chart covers the load hanging FROM the boom tip ONLY, there is NO load chart for a jib, the LOADING on the jib puts a LOT of stress on everything, that is WHY the JIB load charts ARE a LOT less then then the main boom.
I have been operating cranes (little to 500t, short boom to 350') since 1961, long before OSHA, I have seen ALL types of home made "jibs" put on the end of booms back in the cowboy days of cranes operation, it was thought this was ok, the trouble was a LOT of cranes came down BECAUSE of these "jibs" which in turn KILLED people at worse case, and hurting a bunch more, now days the owner and YOU WILL go to JAIL if you are operating a crane with anything homemade on it and you hurt or kill someone, The OWNER and I would GET fined just for operating the rig with the homemade stuff on to, this is even if no one is hurt..
You can argue all you want but the FACT remains the a crane (a military wrecker is a crane) IS designed for a certain load FROM THE BOOM TIP at a certain distance from center of rotation, this design INCLUDES EVERYTHING from the base mounting UP, NOT JUST the BOOM.
You guys do what you want (you will anyway), but REMEMBER if you modify the crane in anyway that is anyway OUTSIDE the design specs.(jibs, ect.), and somebody gets hurt or killed, there IS 99.9% chance that you will be a bunk mate with Bubba.