While I have not done it I am sure you can dilute 30% to slow the process.
I tried molasses and besides strong odor it takes a long time to clear rust.
Model A-s are the image of what antique cars should look like. They get driven a lot because they are very streetable while most antique cars just aren't. The huge production numbers plus the survivor rate is extraordinary. Try and find another manufacturers car from the same era. None survived