Looking on nFlow's website, they only list one engine for the 570 ACE, RGR, and RZR so I'd be pretty confident they all use the same engine. If you can get the serial number off both engines, Polaris should be able to tell you as well.
I had to replace the crank on my 570 ACE, that engine is pretty straight forward if a rebuild is necessary. There is one blind bearing that's kind of a pain, but nothing to be too intimidating if you need to go that route.
You say straightforward...that's alot of small parts for me to screw up lol. I explored that route and messaged someone on ebay about a rebuild kit and it listed to 2017 so I asked and he said the crank is different on the 2018. I asked if that meant internal or external where clutch goes on and he still hasn't answered. I will never understand why polaris wants to stick it in their customers so bad. I bought a 1996 jeep for the trails in the meantime...just to keep from giving the dealership the satisfaction of taking my 2600 bucks lol.
Don't get me wrong, there's a lot of pieces, but with a single cylinder there is only one place for each of them to go. I used a MCB kit when I rebuilt mine. I just checked their site and there was a crank change, but it was the stator side. So if you get an entire engine it won't matter, but if you do rebuild, you'll have to be sure to get the correct crankshaft. I'll attach a link and you can read their note on it. Changed mid 2017 it looks like.