Here is a general overview:
The R body was pretty much a heavily restyled B body (like the 78 Fury and Monaco). Slightly different dimensions, lots of weight reduction, and no more big blocks. But underneath was the same isolated B body structure that started in 1973.
1979 offered St Regis and Newport police cars. The police R bodies were all V8 powered (unlike the civilian ones that offered the slant 6). The police engines were the 318-2 and 360-4. I don't think there was a 318-4 police motor that year, except with California emissions. Rear axle was a 9.25" with choice of 2.7 or 3.2 gears.
For 1980, the Newport left police service and the Gran Fury entered. Federal engines remained unchanged. California lost the 360-4. The rear axle changed to a 9.25" ratio with no other options.
For 1981, the federal cars lost the 360-4 and the 318-4 was the top engine.
Mechanically, it was basic stuff. HD engines, 727 transmission, PS and trans coolers standard. Oil cooler optional, sure grip optional, relocated spark control computer (to the inside of the car) optional.