"Back when" I had the same cam, lifters, pushrods and 273 rockers on the 340 as I have right now on the "low buck" 318, that thing used to routinely see 6K and sometimes more in mud holes. Once a year turned out to be plenty. I ran the you-know-what out of that thing
So far as compression tests
On an engine you have acquired and don't know history I would ABSOLUTELY set the valve lash if they are adjustable.
I do NOT believe in this nonsense of arguing with a hot, running engine, it's completely not necessary. If you memorise the "EOIC" method, you can correctly adjust anything that has pushrod valves, from a 1 lung Briggs to a 4 -row aircraft radial.
EOIC means that you rotate the engine until
the EXAUST just starts to OPEN, and set the intake on that cylinder
Then rotate until the INTAKE has opened and is nearly CLOSED, and set the exhaust for that cylinder
On a V8, you can warm it up, pull one side, and go front to back, install that cover, re--warm if necessary, and pull and set the other side.
On a slant, simply look the situation over and get things prepared for a quick removal, warm it up, pull the cover, and set the valves.
I use the proper feeler(s), as well as feeler(s) about .002 larger. The correct feeler should slip right in, the .002 larger forced or not at all, IE a "no go" gauge.
Perform hot
Try to check each cylinder in the same manner, IE same number of compression "pulses" and be sure you crank enough that the gauge peaks.
Block the throttle open.
Any that are questionable, squirt some oil into the cylinder and recheck. This checks for poor ring seal. Be careful not to get too much oil, which will raise compression ratio!!!! and give you a false reading