Mark, there's been many many renditions of the Norvel engines. Cylinder differences,piston differences, porting differences, venturi differences. There's also crank shaft differences where the web of the shaft has been lightened on the perimeter of the crank web while others are solid. Deck heights of the case are all over the place with these so you could own two identical engines and they perform differently. I have seen a lot more differences with older versions than the latest versions.
So to ask a question in regards to performance, it's not exactly fair to offer rpm mentions unless one knows exactly what you have. Just looking at the top view of the two engines shown, I can tell you there's a immediate difference between the two needle valves. They both operate differently due to needle shape. I have had good success with the version on the left but the version on the right has been questionable at times depending on when it was made. As soon as the needle gets the engine leaning up, it cuts off fuel supply and falls off rapidly as if the taper is too aggressive. Some work, some don't work .
The other is what you desire to use the engines for. You can't assume that the engine is what came in the box or packaging. Norvel was notorious for mixing this up especially the Revlite versions that came in the red. white boxing. It was so bad, that they were selling these engines at $20 a piece to get rid of them, units that came in damaged boxes were $5 cheaper. I acquired 10 of them at these prices and as mentioned, incorrect instruction manuals, parts were mix matched, AME's were in Big Mig boxing. You need to remove the glow plug and count the port holes in the cylinder. 5 small ports for a Big Mig, 3 larger ports for a AME.
A HUGE problem with the AME is the wrist pin. If one had a used engine it might not be fair to assess the engine unless one is insured that it doesn't have a score in the cylinder. The wrist pins are staked on these engines. When the piston wears, the staking is compromised and the wrist pin slides fore and aft. The wrist pin hole on the AME version lines up with the porting hole in the cylinder. This can score the cylinder and it can get caught in the port hole if it slides into it. This can't happen on the Big Mig as the cylinder holes don't line up.
AME engines are not going to run properly on suction, the venturi is too large, and it will run best on bladder however many successfully ran them on muffler pressure. Norvel did make a backplate for crank pressure but the hole in the pressure nipple was too large for it too work like it should. The screen cap on top of the ventui is difficult to remove on the older versions which makes it difficult to determine venturi sizing. The older Norvel's like you pictured on the left also have their ventui glued into the case. This is a area that needs to be addressed or problems will occur. Removing it,cleaning it, and gluing it neatly back in with JB weld resolves any problems. The Revlite versions mainly had their venturi's bolted in with a oval shaped o-ring under it. All of this is relevant because one can't offer performance statistics until these issues are not a issue. Don't tear it apart, just insure that it's tight and the venturi is not wiggling. If the venturi is wiggling it's sucking air and it will become looser and the threads on the through bolt will chew the case up in short order.
I have found the left engine with the squarish cylinder head style which I believe is ABN to be a very pleasing engine. I really appreciate the right cylindrical style Revlite versions but they require some techniques in breaking that unless followed can determine a short lifespan if one is not familiar with them.
I have two heli .061's, the differences on mine are quite different as the heli .061 had a bronze bushing in the case which was fit quite tight and requires lots of break in time to loosen things up. The venturi in my opinion was also quite small and I have opened that up a bit. I'm starting to see rpm numbers that are more in my favor for what I'm using them for. I also had the case honed to eliminate running the engine a bazillion times to run it in.
Seeing that you have so many of them, I would run them all and document their engine rpm's between all of them and determine which of what you have starts the easiest. This will certainly ease making a choice of which one to use later on.
Just another note, the engine on the right is using a Merlin plug. Different head styles can offer a 500-800 rpm increase over the stock unit. I personally haven't had a real positive experience using the Merlin plugs in the Norvel. Many have, but not me. That plug requires 4-5 additional head gaskets to work. I have had that plug do funny things that I don't care for. I have had it start without the battery connected and I have had it backfire instantly when the battery was connected to it. It's a very hot plug in my opinion too hot. I never understood why Merlin offered a hot plug for the standard 1/2A drop in element. I contacted Al in regards to this as he offered the blue insulated version for 1/2A r/c. Too me, the colors are backwards. The blue being cooler in my opinion would be associated with high nitro fuel where the red indicates hotter for lower nitro fuels and better idling characteristics. I strictly use Nelson plugs in these engines and have no reason to try anything else, they're the most inexpensive plug not to mention the most durable and reliable.