I really hate the idea of using a 90 V battery in a stuffed dog. First of all, 90 V is enough to give somebody a very nasty shock, and I doubt this dog has UL-approved wiring. Second, it's bad form to take 90 V and then throw away most of the energy supplied by it just to heat some series resistors to step down the voltage. Why not use lower-voltage batteries to start with? (The old boyfriend doesn't seem like a natural at electronics.)
As for the bulb, you may be able to get LEDs that work very well at low voltage, and last a long time. I'd search around for LED blinkers. LED blinkers are routinely used for bicycle lights. You may even be able to just modify one of these standard bike lights for use in the dog, and get rid of the old circuit.
25 years ago, the age of your dog, the preferred blinker was the neon bulb NE-2.
I remember it well. Unfortunately, the voltage needed to fire it was in the 90-100 Volt region. But as Mike says, these days there is no reason to use it. Much better to use LEDs at several Volts. Easier and safer. LeeH
(published on 08/24/2009)