very good question... after all my searching and reading of old conversions i have never seen anyone do that. most people hunting heilands go for the model with the correct bulb release already. the hardest part is finding the correct end cap, well can't really say "correct" end cap, but closest to accurate end cap
Mine's not an MR or any FX, in fact it is just a Heiland Conversion, with a "close to accurate" end cap as halliwax would say I did mess around with using the internals as a natural blade plug. It would most likely fit as long as you had all the correct hardware to secure it, since it would definitely fit inside of a 1.5" flash tube.