Is your Model 20 the children's version? I found a lot of videos on the Model 20 that you might could use or learn from. I hope some of these help. You might also try a library for a source of information.
https://video.search.yahoo.com/yhs/s...r=yhs-mnet-001
I found this today that may help you. It's not the original Adjusters Manual but looks like it would help you. Maybe you could contact Suncatcher in League City, Texas & ask about the manual before purchasing it. Just to make sure it's a good, readable copy. It says in the description...
"In depth manual for the Toy Singer - Model 20-1 with an Oval Base or the 20-10 Model with a Rectangular Base. Contains same information as original instructions plus lots more. How to time your toy is explained and more in the 16 pages."
https://www.suncatcher-tx.com/shop/c...-x32214643.htm