Just as a qualification, tho- I dislike all inter-marque engine mixing.
See, there's this primary and heavy emphasis on engines as 'the car'. To me, engines are far less important than sheet metal and chassis and other design criteria. Short of racing, and with the hood closed, all engines twist a shaft.
I know and love AMC engines, having literally owned nothing else since 1973 with three exceptions (one of them a Stude, and the other two mere hood-closed commuter-boxen).
In any case, I don't care so much about non-AMC engines; why is everyone so hung up about that tiny subset?
What about a class for mix'n'match all AMC/Rambler cars? Or -- heaven forbid -- hand-made modifications?
Nearly EVERY AMC/RAMBLER OWNER I KNOW has a customized car. None of them but me ever go to Nationals. All of us have non-factory-stock cars.