If you bought Craftsman's most complete toolbox set in 1968 it came with a set of tappet wrenches. I know, I bought one. They are probably the least used tools in the box. As someone else pointed out, you can make your own by grinding down some open end wrenches or try using ordinary wrenches, unmodified. They usually work. Another way to adjust valves is to go down the line and check them, mark the ones that are out of adjustment with chalk then go back and just do those ones. If you service your engine regularly the ones that need adjusting varies from none to 2 or 3. And they only need a slight adjustment.