If it's just a competition for the 'loudest box', then by far the easiest and cheapest solution is to do a Bumpboxx and just build a big Class D mono box.
TBH, no vintage factory box can hang with even a low powered 12V class D box powering high efficiency drivers and tweeters.
A comp testing the 'Best sound quality' can tend to be a little too subjective for the varying tastes of people. Most people will agree however, that a big Mono box won't win a sound quality comp.