hi there Lew
I have a feeling, my friend, you may have to bite the bullet with this one and alter the gearing to slow the crane down. I have been reading back through the posting and it does look like an 'all in one' circuit board that you are working with - very difficult to alter / tamper with.
I suppose though the other alternative would be - to gut the old electronics out and replace with say a Futaba receiver. Then, you would obviously have to have speed controller for the tracks on one channel (forward and back of the actual movement of the crane) - then you would require the other 3 channels for the operation of the crane itself and they could be done with small, cheap, speed controllers.
I have done this myself before on a model - but - for the winches on the crane, I used continuous rotating servos with drums attached for the cables & etc.
The speed controllers I bought came from a local Company - and I will try and find the link - because it is a long time since I made this model. I can put the link on for you if I find it.