My guess is, it was not done like that because nobody used an off the shelf starter in that configuration.
Proper and bold labeling would be imperative.
The work to convert the starter is much more labor intensive and technical, than changing the under dash relay.
I agree 100% with why it was done the way it was.
I have been driving my M1028A2 for five years now, daily during the winter, occasionally in the summer.
With nothing more than maintenance.
However the starting system is a different story. Did your relay modification and still had an intermittent
No start problem.
Changed to Chinese Starter, all good for a year or so then same problem.
In the meantime I had the Delco checked and found an open commentator segment.
Refreshed with new armature, I pulled it off the shelf and installed.
Problem fixed, well not exactly. better but still acted up on occasion.
Changed the relay again, perfect for over year. Then same thing, intermittent no start.
So now I'm on my third relay(I blame China junk)and now I will locate a 28MT 12V Solenoid and make the change, connect the Purple and Purple/white
Together and give it a try.
I will indicate the change on the starter, and in the TM9-2320-289-10 Operators manual in the glove box.
Tom