If you take a look at the article that Ross cited from the
February, 1956 Service Counselor, you'll see that the modification was offered for 54th Series Gear Start and 55th Series Twin Ultramatic. Ross has extended the underlying logic to further tailoring and into the 56th Series.
Because both modifications involve only the rear upper valve body, the work can be accomplished with the trans in-car, with the pan removed. However, I don't think a packaged shift kit is necessary.
The shim for the direct shift valve piston can be fabricated locally, but the SC image isn't very clear. Perhaps Ross could indulge us with a pic of his shim, relative to the piston from a disassembled unit. However, thickness of the shim may well vary, depending on the desired feel, which would require some experimentation on the part of the owner and installer. Thankfully, the Ultramatic pans have a drain plug for capture and re-use of the fluid.
The low-high shift valve spring simply needs a bit snipped off, but perhaps Ross could provide a pic of a stock spring showing the cut point. However, we need to know the length of the stock spring, which is the same for all three years, to make sure someone hasn't already been there and done that. That is, we don't want to cut too much off that spring, which would be irreversible.
Yet, since Ross was working on a '56, I'm wondering what the difference is between the low-high shift valve piston of '56 compared to that of '54-'55. That is, the parts book shows two different numbers for that piston between '56 and '54-'55, but the spring remains the same for all three years. I wonder, then, if Packard engineers were manipulating the length of that piston to change the shift point. If so, perhaps that will affect how much needs to be trimmed off the spring for '54-'55.
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