If it was my loader I would not hesitate to take it to the hydraulic shop and leave it to the professionals. I've rebuilt front forks on motorcycles but that's about the extent of my hydraulic expertise.
I did the same thing with two cylinders on my LA402 loader. Was easier and not much more expensive than just buying the Kubota seal kits and trying to accomplish it myself.
In my case it was the curl cylinders. I got both done at the same time. ONLY because soon after I found the first leaking, the second started leaking.
I would suggest you get both cylinders rebuilt at the same time if you have the funds available. In my case it cost me $100 per cylinder. Seal kits were about $60 or a bit more delivered. So for $40 per cylinder, someone else with experience did the job the right way...was worth it to me, big time.
Edit: You just make sure the loader is situated in a way that it will not move when the cylinders are removed. When you put them back on, if there is air in the system, cycling the cylinders from end to end a few times will purge the air from the system and you will be good to go.