The pic above shows an NOS 1930-31 Model A wishbone on top, and an NOS 1932 wishbone on the bottom.
This is a bottom view, with the weld seams on the tubes facing the camera.
For both A's and B's the perch-to-perch centerline dimension on the bottom side is 37 inches.
The perch-to-ball center-to-ceter dimension on the bottom side is 39 inches for the Model A (1928-31), and 47-1/2 inches for 1932.
The 1933-34 Model 40/46 wishbone is not pictured, however its perch-to-ball center-to-ceter dimension measures about 2 inches shorter than the 1932 Model B, at about 45-1/2 inches.
The pic above shows the inverted "U" shaped cross-section of the forged yoke on an NOS 1928-29 Model A wishbone.
Contrast this section shape to the cross section of the 1930 and later Ford wishbones shown below.
Despite the difference in the shape of the yoke, the 1928-29 Model A wishbones are dimensionally and functionally interchangeable with the 1930-31 Model A style below.
The pic above shows a close-up of the rear wishbone forgings of a 1930-31 Model A wishbone on top, and a 1932 Model B wishbone on the bottom. Both rear forgings are a similar "T" shaped cross-section.
The 1933-34 Model 40/46 wishbone also uses a very similar rear forged yoke shape and section as the 1930-31 and the 1932.