What bothers me is your loss of oil pressure and hard cranking. This points to a bearing issue.
What I would do next is drop the pan and check the rod bearing insert and crank journal for overheating. Then roll the crank over to look at the bore, small end of rod and piston skirt.
I have hundreds of hours working on this model of tractor and never had the need to drop the pan in-frame, I usually just yank the motor. I actually don't know if this can be done without looking at the manual. Just guessing now, you may have to drop the axle wishbone and oil pickup tube to remove the pan.
Look over #1 bearings & bore real close for loose metal particles.