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This was during the Football War (also known as the Soccer War or 100 Hour War), a brief war fought by El Salvador and Honduras in 1969.
"A Salvadorian C-47 opened the four-day war with Honduras by flying a solo bomb run over Toncontin airport, in an attempt to destroy the enemy's pursuit planes parked out in the open. This plane was never designed as a bomber and it was no wonder that their mission failed, considering that they had to roll the 100 pound bombs out by hand through a cargo door…"
It seems that in the face of US embargoes at the time, the Salvadoran Air Force (FAS) managed to buy 7 P-51 fighters from private owners, while the Honduran Air Force had "10-12 obsolete but potent Vought Corsairs F-4U's."
The FAS had also some FG-1/ FG-1D Navy Corsairs, and got hold of the later mark Mustang Cavalier.
And thus the stage was set for the last piston v piston air combat.
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