Determine what the exact problem is before ordering parts..!! Don't want you to spend money for items not needed... I'm just diagnosing through your description, and using the S.W.A.G. system... If you don't know what that is, ask your Dad... I'm sure he knows...
The grinding of trans gears could very well be something to do with the release bearing, and/or the pressure plate. If any of the holes in the torque tube (clutch housing) are open, small varmints such as Chipmunks, mice etc. seem to love to build nests in the clutch/ pressure plate area. Several years ago I removed literally more than several yards of string, nut hulls, etc from the clutch housing, on my 310B Case backhoe.. All that was keeping the pressure plate from fully releasing the clutch disc. Could be a broken spring in the pressure plate, a release finger worn bad, or completely through, and grinding on the release bearing. Possibly cocking the bearing, and making a grinding noise. But, that does not explain why there is no whining noise when going down hill.
The IH part number is ST246 for that input shaft bearing. Crossed it through NAPA, and the universal part number is 6206NRJ.
Checked Messicks online store, and through them the bearing is $37.55. Should be that price at your local Case/IH dealer. NAPA $38, and some change. I checked a place where I usually get NOS Timken bearings, and they want $53 and some change. Ran the number on epay, and showed 3. From about the above prices, and up.
Sometimes the dealer is the most reasonable. That bearing is used in a lot of older IH tranny's.
Keep us posted..!!