Thanks for this discussion. Yes Ive seen some cars retrofitted with custom control arms to make it fit their desired track width while using the S550 center section. What makes a retrofit of a Ford IRS to my West Coast Cobra so curious is that my axle width from axle flange to flange is about 63”. Yep 63. Thats because the West Coast replicas are wider and longer than originals and the rear hips on these cars are huge. It allows 12 inch wide wheels and 13 inches of tire tread on the asphalt. A whole lotta “Rosie”.
But I digress. The WCC uses a rear axle assembly from a full size ford 73-79 car.
One post I found on line ( not confirmed) for modern Ford IRS systems for flange to flange dimensions
Were:
S550 Mustang = 65 inches
Crown Vic = 65.6 inches
Ford Elplorer = 58.6 inches
My research continues.
Thx