The 1A chassis brakes are better than the early type. They are vented which will reduce fade but crucially, the discs are larger in diameter and the pads have a larger surface area.
Changing to the later system is a straight swap of the discs and calipers. The only thing that complicates things is the wheels. The later setup needs the later wheels to match or the calipers hit the back of the earlier wheels.
From memory, the later servo and master cylinder are different too. I could be wrong on that though.
