Odd man out here
I personally would sink the money into something else and just drill and pare them.
I had a large PM mortiser for a number of years. Great machine. Half the time either I banged them out by hand or drilled and pared. Mostly due to odd angles and it was faster than building a way to hold different angles on the mortiser.
Now I only bang them out or drill/pare. If I had a bunch of Arts & Crafts furniture I would worry about getting another mortiser. But it would take a lot of repetitive work to do it.
Take care, Mike
Wenzloff & Sons Sawmakers