Thanks for all the suggestions on fuel level monitoring. My tank is behind an aluminum bulkhead, so a mirror isn't useful. The backup camera system is interesting. I see on the web that the "Pyle" brand gets bad reviews. Costco online has a Rear View Systems model for about $75 that gets great reviews.
Mark's suggestion to label my tank in gallon increments makes a lot more sense than what I did -- mark it in inch increments only to discover that not all inches equal the same amount of fuel. When I bought it the tank had only two marks on it, neither of them labeled.
I don't have the money for an EIS 2000 with fuel flow option, let alone an HKS, as nice as it would be to have either or both. My 503 has only 46 hours on a reputable, professional zero-time rebuild and runs beautifully.
-Dick