Both my timing adjustments (bottom of distributor & plate to block) are fully advanced. Still seems to need a bit more advance though. My question is, can I retard those fully, and advance the gear 1 tooth? And work from there? In other words, does the full range of the adjustments roughly equal 1 tooth on the gear? Thanks!

Yes, you can re clock the distributor another tooth and reset the slotted bracket. I would check the damper to make sure it's not slipped,
and see where #1 TDC sits with your current setting... If the engine is stock and it is a mechanical with vacuum advance distributor,
you shouldn't be past 12 BTDC initial... (if it's a running and functional ESC setup then 15 BTDC initial would be fine...)