SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

You don't have head to head coverage, but if there aren't any dead or dry spots I would let it go. 20gpm means you are probably at 4gpm per head. Find the rotor that you like and make sure it will throw 40 feet at 4gpm at your operating pressure (while the zone is running and no other water is being used, put a pressure gauge on a hose bib). Impacts are going to go bad, so you can change them all at once or buy 5 rotors then wait for them to go bad, or buy one and change them out as needed.

You first will need to dig up the the connection to the white pvc pipe. This will make the hole large enough that you can unscrew your "Can Rotor (RB MaxiPaw?)". The fitting is now just connected to the black poly pipe. I personally would add a fitting- a 1/2" elbow (M thread x F thread), which will give you a very manuverable swing joint.
You will need to know the size thread your existing heads have, if 1/2", and your replacement rotors' threads are 3/4", just use a 1/2" x 3/4" thread by thread bushing. If visa versa cut the 3/4" barbed elbow off close to the end of the barbed fitting and replace with a 1/2" elbow (barb X 1/2 thread), and add 1/2" elbow -(female thread X male thread), giving you a swing joint.
Sounds complicated but if you pick up (5) Rain Bird 5004pc here as well as the proper fittings, cost is less than 75$, and once your look closely how they connect to the piping, you'll get it.

I'd go with swing pipe. The swing joint you mention could leak if not assembled properly.