DavidC,
"But will the retainers remove without breaking." In my experience - No. Out of the fifteen I removed on my '96 only two did not break and they were not really reusable afterwards. They looked just like the one pictured in JLandry's post. Perhaps you could fabricate a thin tool that would slide in and disengage the moveable portion of the clip to facilitate removal without damaging the retainer.
After thoroughly cleaning the insulation pad I reinstalled it using large diameter round-headed "Christmas tree" style plastic retainers that I purchased from a Carquest parts store. They did a much better job of retaining the mat. (The Ace hardware store also had that round-headed style of retainer in several sizes but they were much more expensive than at the auto parts store. )
P.S.,
www.lmctruck.com also lists the O.E.M. style retainer in their online catalog - P.20, PN 55-1130, item #5 Hood Insulation Retainer, '94-02, $.95 ea.