Hey Frank,
The Spitfire axles were super weak! it is no surprise you snapped them in to. The rotoflex system was much improved over the spitfire system however still weak in my opinion.
They eventually came out with a CV kit that fixed the single U joint issue and turned it into a true IRS. However I still do not trust those CV axles for increased torque above and beyond 200 ft-lbs. The axles are real spendy also I would hate to test them out and bust em
This CV kit still did not solve the weak differential problem!
GH