Adjusting valve clearance on a 454 V8.

[paintinx]

Good morning to you all.

I have a 1979 Chevrolet suburban and would like to check or properly adjust the valve clearance.
I hope I am expressing myself correctly. Please excuse my bad English.
The problem is that I hear a slight clacking sound on the left bench and I know it is coming from the valves.

Can you please tell me what steps I need to take to get the valve clearance right?

I only have found this

https://brianbradburn.tripod.com/chevy454.htm

I assume I have mechanic valve lifters.

I read, that I need to turn the engine while adjusting. If I had a manual transmission, I would just put it in gear, lift the car to one side, and then turn the other wheel. But how do I do that with an automatic?

Thanks in advance and have a nice Sunday