Thank you! You weren't kidding, this is one old part. Believe it or not, though, I have run into this before.
There is no easy fix for this. Our go-to so far has been our 39-365, which is a Truth brand operator, but it's going to take a pretty extensive rework of the sill and sill trim to get this to fit properly. The design of the base is just too different. See the image below to get an idea of what I mean.
Even then, it's not a guarantee. You can never tell what you're going to run into with these old windows and there is always an exception to every rule. The
39-365 has been successful for me but that doesn't mean it will be for you, as well, even after all the work you'd have to put into it.
As for other parts you will need, you'll have to replace the track on the sash, as well. There are two varieties you can pick from, depending on how the new arm ends up aligning with the sash: either the
39-504, which screws into the underside of the sash, or the
39-520, which installs on the face of the sash. You'll also want a new 39-144L handle, of course.
While there is no guarantee, I do think these parts are going to be your best bet. Look these over and see if you think this is a project you want to tackle. I think the biggest hurdle ahead of you right now is altering the sill trim to accept the new style and finding the best position to mount the operator on the sill itself. That's going to take some creative wood trimming and trial and error for positioning.
