Here's a "no 'tude" response to the OP's post:
- A stock 400 is low compression and may tolerate up to about 20 degrees initial timing, but verifying the hot-start behavior will be important to determine how much it'll accept and still start w/o hard cranking
- Total timing considering the low compression and open chamber design is probably limited to somewhere in the 34-36 degree range; California-spec pump fuel is an even lower octane than most of the country (my local pump swill is 93-octane w/ 10% ethanol blended) and that'll probably cap the max advance at 32-34
- Depending upon gearing & converter stall speed, the advance curve should probably start around 1200-1400 RPM and reach full advance out about 3000 RPM
- Vacuum advance should be limited to 8-10 degrees to play it safe; one responder above suggested as much as 16 degrees, but that much will likely cause pre-ignition issues under high-vacuum cruise conditions
- Carb & ignition tuning are tightly related, especially since big changes in the initial timing curve can result in significant idle speed changes and require associated mixture adjustments

The programmable box is a cool unit, but it seems like major overkill for the current application.