I've built a box and most of the parts should be self explanatory in terms of bodies, heads and arms. The casting of the codes isn't always clear, but there's a letter with each part, so the "M" arms go with the "m" body etc.
The only parts are found difficult to ID were the two in the center of the sprue next to the bases. The amorphous blob (Part G1) is the other crawler. It's just a torso with some scraps of a top. It doesn't look like much but once you give it arms, head and a suitably bloody paint job it comes together. The round part next to it without a number is a tray that you can give to the waitress.
I found that the codes are nice for the first set to get them to look like the box art, but to get the best use of the set you need to mix and match parts to keep things looking unique. The only parts I didn't use more than once are the waitress's tray and the lifeguard's rescue can (M-14).