What gear is in the car? At 3k and 500 fwhp I would not hesitate to run a 23 spline box. You will have to make sure the clutch isn't too aggressive however that is true with any manual transmission. Is the transmission all cast iron? It is also good to know if the gears are liberty supplied 9310 material or stock converted parts.
The one i'm looking at buying would be all iron, if it's worn I'd send the stock parts to convert by liberty if they are still nice. the rear is a frankland quickchange, so anywhere in the 3's for cruing RPM's on a 29inch tire. and mid 4's for fund.
It's an old gasser (non mopar) that has radiused quarters but not tubbed and I can run wider easily but dont want it ridiculous-ideally a 30-33inch diameter but as narrow as I can find in a street/slick would fill the radius well. I believe the frankland to be tough, but not glued-track tough, so maybe that's my limit?
The used trans comes with a new mcleod twin disc/diaphragm. The 414 made 480hp/520lb ft on engine dyno. But i know i'll end up spraying it with at least a hundred at some point in the future. Brewer said they'd run 18spline at 600hp &up but if i dont shock it on a glued track, does that give me a cushion to run the 23 with faceplating?