It sure is pricey for that scale (1/50). Wish they had it in 1/25. I tried to build the one from Italeri but ended up in the trash can. Failed project.
This is actually an old kit released through the years as a Snap Tite kit. These photos show earlier releases of your exact same kit (molded in different colors). Why now the box says "glue required", beats me. Probably a marketing strategy to attract veteran kit builders. I've built four of these kits without glue.
I also grew up playing with the original Hot Wheels. This is a great idea of yours. These you have done so far look great. Want to see more! Just for fun, have you thought about putting one in a blister pack like the original little ones?
You must remove all paint from parts where glue will be applied, either by sanding or with a blade. If you don't, the glue will do that and take a lot longer to dry. I assemble all the parts I can and then and only then I paint them.
They were made mostly for that purpose. After all the DM stands for "Dump" and "Mixer". There was the Mack R600 (and a Mack U) which was a toned down version for vans but I don't know if the DM800 had a toned down version.