Ok. I'm going to shift gears and try to guide you a little into what to look for when you view that DeSoto. I have a '47 Chrysler Windsor 4dr.
If it runs, check if it idles at the necessary 450rpm (very low) but is required for it to shift the fluid drive semi-auto transmission properly. If the owner has it idling too high, it's usually because the compression is bad (hard) or the carb needs a rebuild (easy). Try turning down the idle and see if it still purrs. Check the wiring, especially under the dash. If it's stock (like mine) it'll be the cloth wrapped type which if fine unless it is fraying or exposed. They do sell updated wiring kits which are awesome but expensive.
If it drives, check that it shifts correctly from 3rd and 4th, and back down to 3rd. You'll need to educate yourself on the fluid drive system to understand how it works and how to operate. I'll try to find the link that explains it.
There is a lot more but I'll let others chime in....