The incandescent bulbs are 64.28mm (2.53") high, from dome to tip of contact, and 37.97mm (1.495") at the widest.
As I mentioned I have the BA-1156-06 "six gun", warm white, for the main cabin. I like the color and spread; I would have preferred more light output but at the time the 9-LEDs were either too expensive or unavailable, can't remember. LED technology is improving so fast! If I had to do it again, I would use the 9 LED bulbs. With their low power consumption they are awesome replacements for the incandescents.
FYI, I also installed the BA-1156-1142-04, which I think may have been replaced by the BA-01, as v-berth reading lights. Narrower beam, but more lumens.
The only disadvantage is that the LED bulbs are a bit short for our swivel fixtures, and so it can be difficult to get the bulbs in and out.
MarineBeam were good to work with, and as I recall had a good return policy, so you may want to consider one of each to try out before you make a full order....let us know how it works out!