Prism, you're so good with vintage machines - I know you could rig up a 31-15 or 31-20 (my dream ;) ) to run with an even feed foot.
The Juki (98 QE?) and comparable Brother (PS1500?) machines aren't nearly as open as the Tin Lizzie, but you can get even feed feet for them and 11" is better than we can get with most domestic machines.
I routinely do free-motion designs or machine-guided quilting up the middle of king size quilts on my Singer 15 - that might be something to try, too - you already have a couple of those, right?
Granted, there is a LOT of quilt under that arm, but it's do-able.
Good luck! :)