Lull boom cylinder removal safely? Holding valves?

[Hudsons-home-services]

Well got home from the hospital (Our daughter had our second grandson ) and the seal package was sitting on the front porch so hopefully sunday it will get installed.

I'm getting ready to pull this cylinder on my 78-80' lull 644. I haven't had much luck finding a part number or anyone with a seal kit. If you have any insight on where I can get a seal I'd really appreciate it.