look something like mine?
mazda produced a few in 86-87, they were only sold in japan in the 626 i believe, but have heard some made it to austrailia...slightly higher compression than our trucks 8.6:1, rumored in the 9.?:1 area with larger valves. there is a little info on this link, scroll down till you get to the FET engine
to answer your q of how to tell, pull the head, if it has dome top pistons it's a magnum, more than likely it's only the valve cover...