There's a somewhat vague method of deconstructing observed behavior to guess at WOT spark. It's based on the idea that the chamber function will be similar under changing load conditions.
Attach vacuum advance and run with existing curve, motor at full temperature, normal plug heat range, etc.
Monitor vacuum gauge for highest vacuum at 50 mph cruise. Advance until the reading stops going up (i.e., no change), and retard to previous setting. E.g.:
40° = 16" vacuum
42° = 17" vacuum
44° = 18" vacuum
46° = 19" vacuum
48° = 19" vacuum
Use 46°
2/3 of this (30°) will be pretty close for WOT spark. How much is initial vs. mechanical depends on chassis weight, gearing blah.
