Let me chime in here. I use MR 8's from Lightcraft Outdoors... they have MR 8 and MR 11 that match.. same body style, just smaller. I use them to uplight porch columns because they are small and not often noticed. I've also used them on the side walls of an inset front door uplighting and downlighting the area, and I aim the lights to the door from above to light their wreaths at Christmas.
I think it would be a good idea to make a nice MR 8 retrofit lamp. Since the fixture is brass, the fins would likely touch the sides of the body and the whole fixture would be like a heatsink.
It wouldn't have to be that powerful, but enough to cast some nice light on an 8-10 foot tall porch column.