I've had this kit a while, but unsure of where or when I got it. It has photocopied instructions and I was also able to track down copies of both the Testors as well as the Italeri instructions to supplement the original instructions.
The parts map on the Testors instructions show the differences between the original Max issue and the subsequent all plastic retool. The multimedia parts are on a separate cardboard insert and blister packed. They include two rubber tires, various sized metal tubes for the gun barrel and recoil, several springs (look like the ones used in ball point pens), and a few metal shafts, one of which is the axle. Also a small tube of glue is in there. There is no option to not use the metal parts.
I bought the Eduard photo etch sheet for the Italeri kit, mainly for the gun shields. http://www.eduard.com/store/Eduard/Photo-etched-parts/M1-A2-Howitzer-155mm-1-35.html