When my Panel had the 216 in it, 50 was about tops, the thing started to protest and make all sorts of noises. Now with the hot-rodded 235, better breathing, radial tires, etc. it runs comfortably at 60-65, at which point it's revvin about 2800-3000 rpm ... but that's on smooth pavement on a calm day, no transports, cause these things are scary at speed on a windy day. I've buried the speedo but just to see what it would do and there was still more pedal left.
It is happiest at 55 though, just seems to hum along at that speed and gets the best mileage (18 mpg), anything faster just eats the gas.
I'd recommend finding someone who really knows how to set-up drum brakes (dual circuit for sure) and align the front-end to get the best handling out of your Panel.
