Install a PCV system
Sludge under the valve covers results when condensation forms on the inside of the valve covers. The stock Chrysler draft tube arrangement never removed any moisture from the valve covers at all. Since the water vapor insde your crank case rises to the highest point before condensing, installing breathers on the valve covers is a given if you want to prevent sludge from forming in the top of the engine.
I've run a PCV system for years. I plugged the oil filler tube with a rag (there's a pair of bavvles near the bottom that prevent the rag from falling onto the timing chain) I installed a bung in my O'Brien Truckers finned vally cover for a hose leading to a PCV valve and I installed a pair of Offenhauser breathers (a birthday gift from Dennis O'Brien at O'Brien Truckers) on the front of his finned valve covers.
Fresh air enters the front of the valve covers via thye breathers and is pulled down the pushrod holes int the valley and, eventually, out through the bung at the back.
Prior to Installing Dennis's finned aluminum accessories in '93, I ran a set of Donovan valve covers and the PCV valve was connected via an elbow in the bottom of the draft tube (took out the 1/8" pipe plug). The bottom of the draft tube itself was plugged with a expandable core plug (rubber, expandable "freeze"plug") to create an enclosed system.
I've never, in 257,000 miles, had any deposits forming on the bottom of the valve covers.