Gary Hall has reproduced about every part of the Pantera, so I'd start with him. But given the variances between years of Panteras and resulting fitment problems of structural/body parts, you may be advised to fab up your own rails locally. Or try finding a parted-out Pantera with a good rear clip. Note that POCA advised Pantera owners in the late '70s to drill 3 spaced drain holes in each frame rail just for this reason. Plus, a badly sealing radiator cap will vent water out and down the inner fender panel & directly into a conveniently(?) located opening into the right rail. Driving in rain will fill undrilled rockers nearly full as well.
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