I am far from an expert on AMC sixes, but I think the Mexican Hi performance L6 stuff that made it into the US was produced by an AMC-Mexico subsidiary by the name of VAM. Some of it was used on the Levi's "Team Highball" Gremlins and Pacers that ran the IMSA RS series in the early '80s. Serious "Cheater" parts that looked stock but were anything but. Heads, intakes, cams, and probably more. Try Google-ing. Also check some off-road sites as these guys build some pretty hot Jeeps with the 4.0.
I remember the AMC cars at Daytona, they were way fast on the banks, but the Alfas and Datsuns would eat 'em alive on the twisty infield course. I think but am not positive that they used the smallest AMC six available, as the class limit was 2.5 liters, at least for the imports - maybe the I6 was allowed more.
