[HondaDustR]

Yes, compressed air is definitely strong enough, and the valves cannot fall into the cylinder or otherwise fall far enough in that you can't grab the stem to pull them up when that cylinder is at TDC. I didn't have a proper air compressor at the time, but rigged up a big tire compressor that had enough flow to maintain about 40-50 lb. I didn't have any problem with that, but keep in mind that pressure can push the piston down and cause the engine to rotate, especially if it's not exactly at TDC and even more easily at higher pressures. A flywheel lock, or 5th gear with the parking brake set and the wheels blocked should be used.
I also had to rap on the top spring retainers with a hammer to break them free from the valve keepers, since the tapered parts seemed to bond together from being a tapered fit pushed together under constant high pressure. Just small sharp taps around the edge of it, being very careful not to hit the end of the valve stem itself. Then just compress the spring and it will come apart. Once the spring is compressed, if it is still stuck, more taps with the spring pressure taken off will probably free them. Higher air pressure may be needed to keep the valve from popping open if they're really stuck.

Be sure to plug the oil drains with rags, and make sure they're big enough so that there's no way you'll be able to accidentally assemble everything without removing them.

Buy at least a couple extra seals just in case. They usually get mangled if you need to remove one if it got installed wrong, most likely from being pressed on too far. I went so far as to buy a replacement valve guide so I could install a seal onto it being able to easily see when it was at the correct installed depth and I used that for my depth comparisons with the paper clip wire. There should be no excessive bulging of the rubber seal where it meets the metal ring once installed, being caused by the guide going past the little molded step and beginning to spread the seal out away from the valve stem. It's also easier to get the new seals over the valve stems without cutting them on the keeper grooves if you remove the little round spring first. There's of course another special tool used to cover the valve stems so they can't damage the seals, but I can't imagine it's much more than a thin rubber cap or something that can't just be made with a piece of duct tape. I was lazy and just slid them on without anything more than lots of grease. Don't forget to re-install the round spring ring before re-installing the valve springs, and use plenty of assembly lube on the seals so they don't burn on startup.