My two pence:
One could ditch MDC, replacing it with SDC*10 or so to adjust the power levels in Rifts to a straight-SDC Rifts variant.
One might compare the SDC and HP system to the wound points/vitality points system.
I have had alot of thoughts on the conversion as the different books would introduce new Prestige classes. The Core classes would be the original classes from the first book and then would spread from there. Federation of Magic would introduce new Prestige classes and Psyscape would introduce new Prestige classes for the Psionics. I do think Axegrrl has a point as it would be VP/WP system and the different styles of armor would be Damage reduction to the system maybe with a little bit of armor class bonus thats as far as I had gotten on my conversion so far.
I had to put my conversion on the backburner into I introduced the Dwarven Mafia into the OGL system first.
.......really.....honest..... 
