Anyone is welcome to do what they want on their own car.
However, the original factory information is quite clear -
Implementation of the combined distribution block and proportioning valves began in 1970. That did not change the fact that fixed caliper equiped a-bodies did not get metering valves. see here
http://www.imperialclub.org/Repair/Lit/Master/274/page11.htm
and a chart here
http://www.imperialclub.org/Repair/Lit/Master/274/page09.htm
Remained true in '72 even though some other vehicles had revamp in the hydraulic controls. See Pictorial overview of '72 here
http://www.imperialclub.org/Repair/Lit/Master/293/page13.htm
Of course you could experiment with holding off the front brakes especially if they are locking up on icey roads. But I'd look at the lining choice, something hanging up or other reason why they might be a little too grabby before altering the factory design.
edit:
Inline Tube's description is incorrect. For the era we're talking about, Chrysler used a
proportioning valve going to the rear drum brakes. It does more than just delay or hold off the fluid, it keeps the pressure to the rear proportionally lower than the pressure to the front calipers. This is not simply Chrysler's terminology. See for example Fred Puhn's
Brake Handbook, or the McGraw Hill
Automotive Technician's Handbook.
