Don't wane be blunt, but my father had only a hammer a saw and a pliers to take old nails out, he managed to repair everything with it, Oh I almost forgot, he used sometime bob wire to.
Now back to the "screwdriver" just think how often it flipped of and the uncontrolled side forces on the valves, simply no good.
Actually this simple tool is a small piece of tube, drilled a hole in it about 2 inch from one side, with a hack saw (yes I learned something from my father
) cut 2 sections in the length of the tube away.
Now there is place for the rocker, and on the front to take the shim out with a magnet.
The rest you can think yourself, a strip of metal drilled a hole in on side a bit bigger than the round sections of the camshaft, cut on side open, (he again the hack saw
) took at some places some material away so the strip wont touch the head, and welded it together.
About tools, in the picture you see a part of a whole set of tools I designed and made to make out of worn out camshaft bridges good ones, next to be back to the works specific clearance of 0.05mm. after maching they are real in line, what is often not the case
One of the tools out of that set is the Sunnen honing needle, I had it special made to do all the 5 bearings in one go, cost over €1000.00 only that part of the tool set.
If you ever have the chance to measure in that department you will be surprised how bad it can be, have seen GOOD LOOKING camshafts and bearings with over 0.2mm play and not being round by at least 0.05.
Hans