The M head is not nearly as stout as the J; they also take a small spindle taper (7BS, 2MT, or B-3) so their collet capacity is only 1/2" max. If you want to hog a lot of metal with a 1/2" endmill you'll quickly find it's not too efficient.
That video just shows power feeding, you can get power feed motors for around $300. Super nice units, you can walk away and do something else (with table overtravel stops set!) and go fetch a mike or other tool without worrying about even machining marks.
I had a job within the year, involving a long dovetail. The only dovetail cutter I had was a 5/8" shank - too big to fit in my M head mill. I had to go over to a friends to use his 2J2 mill. Running a 1.25" dovetail cutter 2200 RPM feeding 30+ IPM (left an amazing finish even though I was exceeding recommended surface speeds) was nice and all but it was an inconvenience. Especially because I can't drive yet so dad had to wait in the car for 3 hours.
If you choose to convert it to CNC, please keep us up to date on the conversion. I'd like a CNC Taig mill one of these days for engraving and I'd like to CNC it myself as a learning experience.