I use a 40-40A all the time on 16 & 17" aluminum & chome covered aluminum rims. (Putting on factory style tires). If the 20-20 has the style arm where the top arm that doesn't contact the top of the rim, and you use the nylon/plastics ( you buy) that cover the rotating part you use to peel the rim on & off the rim, and you're carfeul, you'll be fine.
I use a rag where the circular spinning nut that holds the rim down contacts the wheel. Protects the wheel from damage.
If you have the other style top arm, you'll either have to change it, or count on using that machine on steel rims only. If you're looking to use one for super low profile tires, I wouldn't recommend it.
If you don't have the air blast, that will be alot of fun on some tires!