Not sure if a new 351-C dipstick is available anywhere on the planet, but the dimensions are in the TSBs (the 2nd one on dipsticks), and Ford has hundreds of longer dipsticks available almost free at wrecking yards everywhere. A 351-Windsor stick from a Van is about 4 feet long! My custom one came from a 1-ton Diesel truck and you need not be a machinist to cut one down and remark it.
Besides the good reasons listed, the main reason for running an Aviaid 10-qt pan is for cornering, even on the street with a stock skinny-tire Pantera. Aviaid or Armando pans have far better baffling around the pump pickup, an in-pan windage tray and a better crank scraper while not hanging down to reduce road clearance. All stock pans allow oil to slosh away from the pump pickup while cornering. Air bubbles & oil is nowhere near good enough for a 351-C.
I saw a 'vigorously' driven Pantera with a stock pan lose it's crank bearings in a 2 hr open track event. If you ever explore the outer reaches of the tach, back in the '80s Mike Cook's dyno experiment with transparent rocker covers showed that without modifying things, oil drain-back was slow enough that 5000 rpms for a few minutes would fill up both rocker covers, leaving only one (1.0) quart out of 5 in a stock pan. Kinda scary at todays overhaul prices....