Can you chain the hoist onto other parts of the structure and use it to aid in its own disassembly?
At work we have a 60 ton one that's around 40+ feet in the air, I didn't see them assemble it though. Our heavy mixer bodies weigh around 110,000 lbs, they use the lift to set them in place and work on them.
You might get some good ideas from your army rigging manuals :-)
Now is the time to work on your welding skills and make a pair of A-frame risers to fit on the forks of your fork lift. Make em 8-10' tall with a U shaped top out of heavy material. Put em on the forks, lift em up and cradle the span before disconnecting. Being sure that the crane is within the weight range of a single forklift..not just
Use decent Sched 80 pipe for the A-frame legs. Id suggest making each one in a pair of tripods for strength.
Mounted on a single lift of course. You wont use em a lot..but you will use them several times a year and they can be used to lift Stuff to the roof etc etc
And set em so your fork is all the way back when level. NEVER leaning away from the driver. And safetychain or straps are suggested.
Depending on the weight of the crane..grabbing it at the center with a single forklift may do the job. May...operators discrestion of course.
Take some of the mountains of steel stock you have and weld up a cradle that slips onto the forks of your forklift (rectangular tube or C channel with straps at the bottom) and adds enough height to pickup the crane beams. When I installed the new roll up door in my shop expansion I had to similarly crib up my forklift due to mast clearance issues.
Obviously watch your center of gravity i.e. lift that beam set in the middle and after disconnecting just lower it straight to the floor, back the forklift out of the cradle and then re-pick the beams with the forklift normally.
I would do it similar to what Gunner and Pete wrote, but, I would build a box made out of 4x4 lumber on top of a regular sized pallet. the box would be sized to fit around the winch and still be tall enough to catch the traveling member before the winch bottoms out.
Then your forklift will be able to hold it while your guys unbolt it.
For the gantry i-beams: fab up some Y receivers to mount on the forks and hold the gantry well above the forks (maybe not as high as the mast, but whatever works), weld a safety chain on each, and use them to pick 'er up and lower her in unison. I suppose the same jigs might work for the front/back i-beams, too.
I'm sure you'll have already dismantled any weight you could easily take off, like the hoist and motors.
The manuals are about lifting, doesn't matter if it's 10 tons of bridge crane or 10 tons of military equipment. So what if you connected a chain hoist on each side, lift the weight off ends, unbolt the ends, and lower to the ground with the chain hoists?
Did you get your weighing pressure gauge figured out? I was thinking you can exert some lifting force with the fork lift and see how much weight is involved to lift different points.
Page 6 has some methods of lifting the crane for disassembly or assembly.
Nice Idea!...assuming there is back cage clearance on the forks. That pesky grill work above the forks themselves can often get in the way on this sort of lift. Sometimes they are bolted on and you can remove them..often times they are welded on...
Go up and remove the hoist and it's carriage. Grab a couple sets of chain falls and use them to lower the bridge by connecting them to the carrier tracks on each side. The bridge should come off easily by removing the bolts that hold the carrier bearing saddles. Now remove the traveler drive and the carriage from the tracks. Then unbolt and lower the tracks. For that you can clamp to the structural beams with a section of I beam to distribute the load and attach to that.