These frames will always be remembered for using fork legs for the rear suspension.  At the time, it was a fairly elegant solution.  Most of the parts were already being produced for the legs so they just needed to clamp them in a special "crown" and plug in some "drop outs" to attach to the lower swing arm.  It seems like the aluminum was pretty soft or the heat treating was flawed since nearly every frame we run across is cracked.  If you plan on buying/riding one, check it carefully for cracks. (this one is the first one out of three that we have owned that is NOT cracked!)