Found a new mechanic who actually knows VW engines (and drives a '63 Beetle himself). He discovered that the electric fuel pump I'd had installed was mounted wrong, was wired incorrectly, and wasn't the right pump for my engine in any case. He swapped it out for a stock pump, cleaned up the wiring (including a loose one that was the reason my tach wasn't working) and a pinched hose leading to the fuel filter, adjusted the choke slightly, and replaced the master brake cylinder. It's amazing how much better it stops now that the rear brakes are functional! The engine is running better than ever. Tomorrow I'll get it inspected, and then -- weather permitting -- I'll be cruising again.