The line for a compression tester works great for an air line and fitting. Makes it easy to turn it in.

For me, I get all the rockers off, then apply the air and let the motor rotate to the bottom. Whatever the compressor has is what the cylinder gets. If it can survive fire, and whatever pressure that makes, a compressor hasn't got a chance of hurting anything. The more air pressure you can muster the less likely it is to accidentally open the valve.

I have also always used air and never had a problem. The rope deal works, but is more trouble than it's worth to me.
It would seem to me that if you can get a screwdriver in the spark plug hole, you should be able to get your air fitting in it?

Edy aluminum heads, E Body Challenger, TTI 2 inch, angle plugs, completely impossible from above on number 2, 4, 6. Same applies to a compression gauge,,,,screw in and rubber tipped cone fittings. If you know a method that I do not, please share. Incidentally same applied when engine had stock heads. Would love to know how to check compression on these cylinders. I posted before on this forum, this question. Received zero responses.

Also using normal sized philip screwdriver, you only need to get into 4 cylinders, not all 8 as required with air or rope technique, both of which I have used in the past. To each his own. Easily get screwdriver in 1, 3,5, 7, 8 which generally all you need,,,,as again 2 pistons will be top up simultaneously.

For me screwdriver as suggested is much quicker, definitely more secure than the risk of ever losing air pressure and having a valve fall into a cylinder,,,,sh**t happens. With piston down,,,I have seen 3 ft of rope sucked into a cylinder.