I've never seen a tractor with breaks on the left hand side? Would be very bizarre to begin with and I don't know I'd want to trust my left foot with breaking in an emergency.
The MF135 and it's cousins all had left foot clutch right foot accellerator and brakes.
Many tractors didn't even have foot pedal accellerators - all you had is the hand throttle.
And personally, driving (real :licking

ag tractors every day, I never touch the foot throttle all day, just use the hand throttle normally in the arm rest. No bumping of the throttle on bumpy ground then.
But then again, I normally take my boots off in the cab and rest my feet annd socks on the front wind screen ledge. Brake pedals aren't really needed these days with exhaust braking and powershift transmissions.
Also, just for the record, split brakes are something that pretty much went out the window in real tractors when 4wd came in, sure most tractors still have them and they are normally left unlatched, but they make so little difference with 4wd engaged, and when it's not engaged, it just tears up the grass.
Only time I ever use them is when I'm working on some scary steep banks and you have to keep the nose of the tractor pointing up hill a bit to maintain positive traction so you don't slide down to the bottom.
Split breaks are also very handy when your on the steep stuff, and when you feel the uphill wheel lift - you nail the downhill brake, and the nose of the tractor will come around, you drive to the bottom and continue on your way

Thats why we leave them unlocked unless on the road.