Many older plans were provided for lathe-only users – as mills were not so common.
I use my mills for more operations than my lathe.
It’s a bit like woodwork where the router can be substituted for a saw, planer, drill – and likely more power tools.
After all, a lathe can have a milling attachment fitted, just as a mill can be fitted with a rotary table…
Did that particular project raise any special operations to make it with mill only?