Micro-Mark sells a circuit board that is 1/2" x 1-1/2" with the height of the resistors and capacitors at 1/2". It is made for a lighthouse model and has an adjustable rate. Haven’t checked lately but I think the price is around $25.00. It comes with a transformer and light. I think there is a place on the board to put a steady light too. We have a porcelain lighthouse on the stereo in the living room with one of these set-ups. I put an small micro switch in the line also so we can turn it on and off when we want. Works great. Hope this helps.
Check your LHS model railroad lighting section, Smeagol… LEDs, Grain of Wheat, and Grain of Rice bulbs are all over the place. Look for HO or O scale EOT (End Of Train) lights for LED flashers… Caboose light sets are available too…
It probably wont be more then an square inch or so and maybe 2, at most, tall, and it has to have an inner box inorder to keep the flashing top light from interfiering with the ones on the sides so yea, pretty small