According to my copy of Frigidaire "Tech Talk" condensed service guide covering dryers made from 1952 through 1960 there were two models of DI-56 dryers.
Imperial dryers DI-56 and DI-57 had Radientube Heating Units at 4400 at 115/230 volts
Imperial dryers DI-2 56 and DI-2 57 had wattage 1550 wattage at 115 volts.
There are other electrical wire diagrams besides what you've got on back of dryer.
Here is what manual says about wiring as viewed from rear of dryer.
Off terminal block you have three connections:
From left to right "B, W, R"
Manual states for 115 volt service to use only "B" and "W" connections only.
"Connections for 115 volt 2-wire use package 5876626"
"Note"
" Connect Yellow Wire To Neutral White Terminal for 115 Volt Service Only".
" For 115/230 Volte Service Make Sure That Yellow Wire Is Properly Insulated From Terminal Block Posts and Metal Frame Parts."
Leafing though manual it appears all Frigidaire condenser dryers well into early 1960's models offer 115v or 120v connections along with standard 115v (120v)/230.
Manual does state by 1958 change was made to heating elements rating for all models. Furthermore on "Deluxe" and "Imperial" models further protections were made on both sides of electrical supply to eliminate the possibility of the heater elements remaining energized with 120 volts should the heater short to ground.
So there you have it, your dryer appears able to run on 120v, and providing you have proper skills (which you do), and wiring can handle load, have at it.
IIRC these condenser dryers weren't exactly fast even at full power. Cutting things down to around 1100 watts means things will take longer to dry. You can speed things along by using highest final spin speed your washer (or washers) provide.
Personally have been there and done that, the excitement of getting a new "toy" hooked up to see what there is....
www.automaticwasher.org
