The 56 input shaft has a fine grove, and the 55 is not. That is one of many changes fron 55 to 56, no they will not interchange.
I do not know on price, but call around, use the PAC yellow pages, and
http://www.ultramaticdynamics.com Ross would be another one,
There are others, around to check as well.
I can not tell you about their work, because I have not used any of them.
EDIT: found another one to ask,
http://www.restorationhydramatics.com Again, I do not know about the work, just saw the listing.
EDIT: I had heard of another guy somewhere in Kansas or Missouri, and I can not find the information. Does anyone else know?
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