The most obvious difference are the woolen cuffs. The velcro has been taken away and these cuffs attached. Upon closer inspection, you'll notice that both right pockets were removed. This was done to prevent a sling or webbing from getting snagged on the pockets, hindering proper weapon usage.
Custom pocket above right breast, most likely for a compass. Note how removal of right breast pocket was not wasted, with a zipper added to create a pocket reminiscent of the newer-issue smocks.
Close-up of modified pocket areas.