iinboard and outboard drums - It's the mounting location on the hub flange. Inboard drums are mounted on the inboad side of the hub flange so the hub and bearings have to be disassembled to change brake linings. They probably disappeard in the '80's.
Outboard drums are mounted on the outboard side of the hub flange and can be removed by just sliding them off the wheel studs - makes life easier. Wouldn't be noticeable on a model truck but cool that somebody has heard of them.
Typical drum size is 15X4 front, 16-1/2x7 rear(?memory test) - thats the size of the surface that contacts the brake lining.
front brakes don't have the dual chambers - no parking brakes on the front axle.
Most of the AMT kits were originally made before Federal regulations required front brakes.
The instruction sheet that you show is typical and front brakes could be sourced from any kit of the same vintage with front brakes. The truck manufacurers all used similar pieces from the available brake manufacturer suppliers. Just stay away from the wedge brakes on the White Frieghtliners. CF was about the only fleet that I can remember that ran them.