I don’t know what the internal seals are in those two jacks. I have a wild *** guess, but don’t want to lead you to wrong info. There are simply too many variations of the dual pump design, I think the only person who has a catalog is hcrcnow.com. If Im looking to find out about the internals of a jack. I usually start with that website, since it’s probably the most complete parts catalog I’ve found on the internet - A good resource to compare things. It’s clear that Lazzar has put a lot of effort into making that website (FWIW, Some of his info comes directly from GJ). the website still has the owners manuals for the 2 jacks - you can look at the parts list, and see for yourself if you think they are same jack. Unfortunately, it looks like the seal kit for the arcan xl2t and the sunex 6602 you’re referring to has been “discontinued” on their website. I don’t know if he has ever had a kit, is out of stock, or if his source is no longer providing them. If you must know, you could consider trying to contact hcrcnow.com. You could give him a PM here, as he is a GJ member (I think he rarely posts).
I think you’ll find many old GJ posts from Edgar and Hiball discussing U cups vs. O-ring/retainer seals. I think Edgar once went on a massive rant dismissing O-rings which I found quite funny. At the time, I didn’t think much about it, but over time (as I have much less experience than any of those guys) I have personally come to completely agree that U cups have better longevity to O rings. Leather cups and stacked chevron seals have pretty much disappeared from current day floor jacks. If you’re looking to read more about current day hydraulic seals, you could consider going here:
https://www.parker.com/literature/Engineered Polymer Systems/5370.pdf