G'day Bob. Top of the morning to you
Good milling spindles are relatively rare and never really caught on, possibly because of expense and stiffness issues
Drummond did a nice version

I'm currently try to improve a lathe milling slide by squaring it up into a box section (latest pet project) so it is not unlike the box section on a shaper, you can even use the tailstock as a support leg
If it's good enough for a shaper then it should be good enough for a milling slide (in theory)

Milling slides are limited but can be used for light milling

A man with your skills should make light work of any improvements.
One big issue if you take the milling spindle route is torque, you need lots of torque to mill steel
GL