Quote Originally Posted by Matt167 View Post
8.8" Ford IRS would probably be the easiest to locate since some Thunderbirds and Lincolns also used an 8.8" IRS, but those will be 28 spline units, and I'm not sure how much HP you are planning. a 31 spline 8.8" out of an Explorer is plenty strong, but that's not IRS and not what you need.
I think the Explorer went to IRS in '02 thru current and should have 31 spline axles.