Aug 06, 2015 · The Thunderbird IRS is often used for IRS swaps for trucks, but the issue with using it as is in the Comet is the width. The track width on the Comet is a scant 54.5 inches, where the T-bird is rocking 60.2, which would put the hubs past the rear quarter panel. The Factory Five IRS cradle also uses the 60.2 inch width, unless you opt for the