Update: I was able to use the Mackie control surface preset, which got me 95% of the right mappings to the VS-700c.
The only major issues I can't seem to fix it that my tape transport controls all work EXCEPT for the "go to beginning" ( |< ) button, which does nothing. If I could find a way to map that I'd be perfectly happy.
I'm also surprised that the full ACT data for the VS-700c doesn't seem to exist anywhere. Seems like it should, and that it would be a decent way of future-proofing in case later versions of Sonar somehow break the mapping.