ORIGINAL: Hobbsy
I grew up milking about 120 Holstien cows and operating about 6 Farmalls. We tried a John Deere or two over the years for a week or so, I can't write here what my Dad had to say about them. I can think of only two tractors that would have drawn us away from Farmalls and those were a Ford 8000 and a Case 1030. The Ford had 401 cu. in. the Case had 451, they had identical HP ratings at 101.5 The Farmall 560 in this picture has an M&W Turbo charger on it at 83 hp.
A Sullivan DynaTron is the cure all for starters.
I worked on a neighboring farm (dairy) during high school. They were Massey-Ferguson believers. My favorite was the "Big M", a Diesel. Ah, I still remember the smell of bag balm. <G>
Oh, and if the OP was in the habit of turning over engines with the starter long enough to drain a whole tank of fuel, he might want to take a look at the starter's brushes. Chances are, they need replacing. A simple chore.
Hobbsy is right too. Once you get to that humongous Hobbico starter, the only improvement after that is in ever larger batteries.
Ed Cregger