I used cylinders from here
McMaster-Carr
Go on the low side for pressure otherwise you will build a clever little catapult. I had to send them back and get weaker ones. I think I went with 30 lb but don't remember. I also used the ball mounts from an Escort "Pony" I got out of a junk yard for the hood and trunk connectors. Good luck finding those nowadays. McMaster-Carr has all kinds of mounting hardware.
Remember, all you want to do is help lift them and then just hold them up.
Tim