Used to have a mounted 2 row picker on an F-20, pulled 100bu barge boxes. Aside from the poor gear selection, it worked. Dad & uncle picked for decades with that. They were planting about 20,000population and going for 100-120 bu yields.
Used a pull type NI 6A with an IHC 300 tractor - about 35 hp - and it worked fine with the same 100bu barge boxes. The 300 has 10 forward speeds with the TA, nice to match speed to conditions! And of course the independent pto, world of difference with an independent pto!
Got a NI 300 2 row picker, and some 200bu gravity boxes. The 300 pulled it, but it was a struggle. Ran out of hp when the wagons started getting full or on hills, had to drive a little slower than I could have. Wet conditions was very tough to pull all those different wheels on the ground through even moderate damp hill conditions. Was planting 30,000 population and going for 140bu yields. Could sure tell the harder pull with the thicker populations.
Got a 324, and didn"t try it with the 300. Did try it with the Oliver S77, and had to drive very slow, 1st or 2nd gear, to keep moving - at least it has independent pto so was useable. Just not enough oomph. Happy with a large Ford 5000 or 7700 on the picker - 60 or 85 hp. Works well, can drive right along. Using 34,000 populations, hoping for over 150bu corn, spots of 200 can be in there now.
This is on southern MN clay wet soils, rolling hills.
You can make it work for fun on a few acres with an M. But if you have high yield corn, high population planting, and want to accomplish a lot in a day, the M is gonna be a little small, and lack of live pto will really be miserable.
Just my experiences over the decades. You are on that borderline....