It takes practice. My first hotrod had solid lifters. It sounded like a sewing machine when I got it so I decided to set them. I got about 5 blocks from home by the time everything got to temperature and the valves stopped sealing. It took me a long time to get the hang of setting those.
With hydraulics you are setting lifter preload. That's important to keep in mind. I always do my adjustments on a warm engine where the lifters are pumped. If you don't, you can't determine where zero lash is.
I do them in stages. It doesn't hurt to have them a little on the loose side so I set mine for zero lash + 1/4 turn if I'm not familiar with the engine. Then I start it, get it to idle and let it get up to operating temp. I'll listen for lifter noise and I'll listen to the exhaust for missing in case I have an adjuster too tight. Then I'll give it another 1/4 turn. I don't need to back it off or make any other adjustments because I know they're all at zero + 1/4. Then if I hear the need, I'll give it another 1/4 turn.
On mine, I ran it for several days at zero + half and then I decided to give it another 1/4. That's where I'll stay until I change the head.
Since it won't run, I'd back it off 3/4 and see if it runs. Then once you get the lifters pumped up, I'd find zero and set them properly.
Hopefully this will get you going.
Thanks Andrew! All that is helpful.
I did back off everything and reset the adjusters to just at zero lash (was very careful not to over tighten them). But then I noticed something that I overlooked before…cylinder 6 was sitting with gas in it

So I cleared it out and tried starting again. It almost started, but didn’t stay running. Cranked some more, but nothing. Flooded it again.
Wanted to get the excess gas out of the cylinders and cranked it without spark plugs - boy it was spitting gas from cylinder #6 like crazy. I don’t understand why the gas just stays mainly there (because engine sits slanted to the back a bit?).
Anyway, while I was cranking to get the gas out, I realized that I got some in the oil (valve cover is off). So that got me thinking, that with all that flooding I was doing before And gas sitting inside cylinders - I better check the oil. Pulled the dipstick and sure enough - it smells like gas and not oil…
At this point I removed the carb and gave it couple cranks to clear out the cylinders from gas. Left everything open to hopefully help it evaporate more.
In the next couple of days I will change the oil and filter - don’t wanna damage anything beyond what I’ve already did.
Not sure if I’m having troubles with carb (maybe needle got stuck and it’s dumping fuel again) or because of all the previous attempts I just flooded it so much, that all the gas just seeped through the rings.
After the oil change, should I attempt to start it again or is there other steps I should do first?
I’m definitely getting a bit frustrated and ready to put non adjustable rockers back on and just try running the engine like this (if it’s gonna start…). And after setting the carb right (hopefully), switch to the adjustable rockers and fiddle with them