Work on finding a ruler foot first...I'd be interested to see if one is made for the vintage machines. Learn as much as you can about the machine too, and maintenance
FM on the vintage can be challenging as you're battling 50-60-80 years of someone changing parts of your machine...so I know personally I've struggled in just the normal freemotion.
Can you freemotion on it? Have you just tried doodling on a stack successfully?