Petr, Your gear looks to be within specs regarding the dogs, taking into consideration the difficulty in accurately measuring dimensions.
I've had many years experience in working on the T-84. When I first got my jeep in 1962,after rebuilding the box, it slipped out of second.
Old Mr. Conyard, whom I bought parts from, knew all about that, and he showed me tricks the old timers used to prevent it. This was after checking that the gear and the synchro drum didn't have too much wear on the splines and the dogs. It's not always easily noticeable for the novice, but wear in the first 5mm of the splines of the synchro drum will, coupled with small wear on thedogs of the gear, especially if it's at an angle, will cause jumping out of gear. The thing to look for is a tiny 'step' at the base of the dog, and on the synchro drum, a tiny 'step' a few mm in from the front.
He also said that the bronze bushing in the second gear had to be a snug fit on the shaft - no wobble.
But the main 'fix' he showed me was, outside of the box, to fit the second gear on the main shaft, install the centre of the synchro drum, then the circlip (snap ring) on the front, and check the amount of forward and back movement there was with the gear.
There should have been very little. He didn't use a feeler gauge, but I'd estimate about 0 to .003".
If it was too big ( which it was on mine, he'd cut and file up a washer from tinplate or thin steel, with cut outs inside to match the splines on the shaft. He'd then grind or file it so that when the circlip was fitted in front of the washer, the gear had no fore and aft 'slop'.
Then, when he'd assembled the box, he'd check the brass synchro rings to see if they were too close or too far from their matching cones on the input gear and second gear. He'd just 'eyeball'to see if there was too much clearance, but he said that if when you turned the rear output shaft, the front synchro ring grabbed on the input shaft, it was too close. He said you should just get it so that the synchro rings were riding on the cones, and just a little push with the selector fork on the synchro drum (not all the way to the indent) made them bind on their respective cones, it was right. To adjust, he'd go through his collection of spacers for the rear of the shaft, and select or grind one to fit correctly.
He's learnt this in the Army during or after the war -not sure.
But he never had a gearbox slip out of second, even with second hand gears.
hope this helps
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt"..Bertrand Russell