Need help with 1970s Lionel HO power truck assemblies - how are they held together?

From what I remember, the copper wipers sit on the edge of the gearbox, and the wheelsets ride on top of them. The bottom retainer cover holds the wheels and wipers in place. It was a real pain to get them all in place and snap the cover plate on. The sideframes were held on by pegs the fit in the gearbox that were very suspectable to being snapped off.

Thanks for your post! After playing around I figured out the wipers rode under the axles and I got the motor to run properly after figuring out the wheelsets'  proper orientation. The pegs aren't intact on these sideframes (nylon would have been a better choice as it would have been more forgiving as far as being able to flex) - my hunch is finding a pair of them isn't going to be easy - I may have to improvise some way to get them to stay in place. 

I ended up getting a Geep carcass and got the side frames with intact tabs. It’s awkward getting things seated correctly - the thought of damaging the tabs was in the back of my mind the whole time.