I'm pretty sure that the Chrysler Fifth Avenue cars had a weird version of the 7 1/4" axle. It had 3" axle tubes, 10" drum brakes and crazy tall gears, like a 2.21 or something close to it. The Diplomat and Gran Fury shared the same body style but the Police cars in those models used an 8 1/4.
That's what I have heard, also. But I have an 88 Diplomat (non cop car) it has an 8 1/4. I also have the complete drive train from a 89 Diplomat cop car That is a 8 1/4 open, and had heard the cop cars got sure grips.
