I like Jerry's companion cylinder adjustment, shown to me by several old friends/mechanics.
It works on most any engine with an even number of cylinders, and with slight variation on any Detroit diesel, even the 3 cylinder.
With this method you're sure to be adjusting the valves while the lifters are on the opposite side of the cam lobes, no chance it is close to the lift part of the lobe.
The alternative adjustment method done with engine only in two different positions should also have all lifters on the base circle of the lobe for adjustment, but some will be close to the lift part of the lobe.. chance for mistakes if engine is not positioned just so, or as Jerry said, with a radical grind cam.
I also like that is is really easy to remember, for about any engine.
First understand that two pistons will come up to TDC together, one is finishing exhaust stroke and starting intake, and other cylinder is end of compression and starting power stroke.
The one starting power stroke is ready to adjust because the valves are as far from being open as possible.
The companion cylinder is easy to spot because as rotating the engine by hand it's exhaust valve is just closing and immediately after the intake valve starts to open. Stop here and adjust the other cylinder.
You can write down the firing order and pare up the two cylinders, or remember what they do if you ever watched the pistons with head off.
The Stovebolt 6 front and rear pistons move together, and the two center ones, and also #2 and #5.
So adjust #1 when #6 valves just move one then other.
Rotate engine more watching for an exhaust valve to close and its intake to start to open.
Adjust the valves on companion cylinder.
Continue, and take notes of which you already did.
This always works.
If you want to look real smart find or recall the firing order, write it down in two columns, first half in one column, second half beside it. Each row are companion cylinders, and you also know which cylinder to watch and which to adjust next. (This is almost required on V type engines, otherwise hard to visualize)
Firing order 1-5-3-6-2-4
1-6
5-2
3-4
