how are adjusters locked into place ? I tried to turn adjuster but it felt really tight , was afraid of breaking it

 

You will neen a regular screwdriver and a boxend wrench that fits the rocker nut. You need to loosen the rocker nut about half a turn and then you should be able to turn the adjustment screw. When you are done tighten up the rocker nut again and the screw will lock in place.

 

the valve adjusters do not have a screwdriver slot only a hex head on them they do not have a jam nut the adjuster is hollow

 

Engine Cold! DX coil wire & ground to block. put finger on #5 intake & bump a little at a time until rocker arm starts to open valve. With engine in this pos you can adj valves for # 1. Intake valve 0.014", Exhaust valve 0.016". Use the following guide to adjust all valves.
Intake Valve Opening On Adjust Valves for Cylinder #
1 5
4 3
2 6
5 1
3 4
6 2

I usually run them around twice just in case, because I hate pulling all the stuff off to get at them. I set them Spring & Fall and she purrs like a kitten.
JK
Edit.
Yes the lock nuts are probably very tight, most people have never adjusted them. Use a 6 point box wrench and you should be ok.

 

In addition to the above: The adjusters are an interferance fit, they are tight so that the lash doesn't back off.