Last night I was going through the bound 1947 set of Illinois Central employee magazines that I picked up on eBay a couple weeks back. In the November issue I found an article on ABLC brakes that the 400 55 ton hoppers (starting with 73600) the IC bought from GATC that year were delivered with. These brakes were different then a standard AB brake in that they had a compensating valve, a larger combined air reservoir, a 12 inch brake cylinder with a 5 inch piston travel, weighing gear consisting of a bar installed between the truck side frames and weighing gear on the center sill. The degree of car loading is measured by the amount of truck spring compression as determined by the amount of travel necessary to move a weighing hook into engagement with the weighing bar.
For modeling purposes the only visible parts would be the compensating valve and the additional piping. I'm attacking the photo from the article.
I was unaware that these brakes existed before I came across the article.