The Enforcers (there were four of them built, BTW) never competed in the A-X competition that yielded the A-10.

The Piper PE-1 and PE-2 (both built in the early 70s, derived from P-51 airframes and both of them derived from Cavalier) competed in the Pave COIN program, which was a competition to find a low-cost COIN aircraft (and never yielded any purchase from the DoD).

PE-1 Enforcer


PE-2 Enforcer (dual control version)


The Piper PA-48s (of which two were built in the 1980s -- new build airframes, not modified P-51s) were the result of Piper and the former President of Cavalier lobbying Congress to force the USAF to test the aircraft as a "low cost" COIN-capable complement to the A-10 fleet.

One of them is at Wright-Patt (N481PE) and the other is at Edwards (N482PE)

Piper PA-48s