Take the crosslide vise off the Y slide. Switch the X screw so that the handle is where the vise handle is. Fab yourself a good sturdy L bracket(angle plate) to mount the crosslide vise to. Remove the lathe compound. Mount the angle plate on the lathe crosslide. You may need a center hole for the compound post and 2 lock down holes for the compound studs.
You will have to shorten one of the crank handles because they get in the way of each other.
Make the angle bracket as right angle as possible. No big deal if its off. Some shims between the angle plate and vise crosslide will even it out.
Once you get the hang of setting it up, you will be able to mill within a few thou.
I used a piece 3/8" steel angle for the vise holder. About 6"H and 6"W for a 10x36" lathe. W/ supports welded .
The stiffer it is the less chatter. Rudimentary, but it got me by until the mill.
If you cant weld, use aluminum plate 1/4-1/2" thick and bolt it together.