I got some time in the shop tonight and was able to get the sliding board jack made and installed.
To make the V-groove at the bottom, I first made two cuts down the center with a rip panel saw. Then I cut a 45-deg kerf from the front / back that met those first two cuts in the middle. Finally, I chopped out the middle section and pared it flat with a 1/4” chisel and cleaned up the slopes with a paring chisel.
Here’s a picture after the first 45-deg cut:
After the second 45-deg cut:
Test fitting the board jack before shaping it and boring the rows of offset holes:
I don’t have a bowsaw yet. So, to cut the curves on the sides, I first made a series of cuts down the side with a crosscut panel saw that stopped at different points in the arc. After the majority of the waste was cut out, I cleaned it up with a paring chisel (bevel-down), followed by a spokeshave, and finally a card scraper.
Here’s the completed board jack installed on it’s track: