The book says you need a factory tool,
but a 10mm socket that's open, a bit of steel tubing and a wrench can be brazed together to do the job.
I used a 3/8 drive socket, 1 1/2" of small (3/8?)conduit and a 9mm (because what ELSE is a 9mm good for) wrench.
Took all of 5 minutes, once I knew what it needed to look like.
Then you use the tool to loosen the locknut, use a flathead screwdriver to set lash (at the cam!) and relock while holding the screwdriver. Not a big deal.

fwiw.
t

'89 V6 4dr- '4- Doris'