I would look at the Delta 50-279 mobile base (26 1/4" x 28 1/2"). Then yourself or a metal fabricator could cut the 28 1/2" length side and splice in some more 1"x 2" x 13.5" tubing to get your 42" length.
The inner dimensions are 17.25" x 36.75''.
This product fits the Delta DJ-20 8 in. jointer.
The base measures 17 x 36.75 on the inside of the frame, so compare that to the measurements of your machine
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