I've rebuilt more than a few of these (and other) transmissions. Here's the deal. If one gear crunches into engagement, its a bad synchro. You have to place the ring on the cone to see how worn they are - trans dismantled. If all gears are stiff, but don't crunch, it's oil. If the lower gears are stiff, then I would suspect a warped clutch pressure plate, or rust or accumulation on the input shaft splines preventing full release of the disc.
Wear on the countershaft will have no effect on the shifting - unless a small steel wear particle gets lodged on the bronze synchro taper. That will prevent normal friction being imparted during the shift.
The shift plates are the three steel items held expanded by the circular springs. They control the detent and the manner in which the mainsaft rpm is transferred to the gear, pushing on the synchro ring. The springs should always be replaced. If the trans makes it into each gear, they are not the problem.
With the trans apart it is easy to examine all of the relevant parts. Swap the 4th and 2nd synchros, and swap the 1st and 3rd. That evens up the wear. Be sure there are no bright particles on the grooves on the inside of the sychros. With new seals and gaskets fill the trans with ATF instead of gear or engine oil. It will shift beautifully. Clean the splines, inner and outer, of the clutch and shaft with WD-40 and assemble. Use no or a very very small amount of grease if you must.