The Strange S-60 is supposed to be much lighter then the original Dana 60 due to different type of cast iron used on center section per Strange web site. Also older Dana 60s vary in weight due to differences in tube thicknesses. Some Dana 60s said to be much heavier then others.
Strange S-60 has threaded adjusters for diff bearing preload backlash adjustment. Old Dana 60 uses shims. Doctor Diff said I could not get a Power Lock diff cause that only fits Dana 60 not Strange S-60? He made it sound like differentials not interchangable?
Dana 60 supposed to be lowest parasitic drag rear diff due to gear design from what I read. 9 inch Ford is said to be very high parasitic drag.
My buddy ran 9s with full interior '87 Mustang C4 auto trans slicks 8.8 rear 35 spline axles. He never had any issues with that rear taking that abuse.