I do have one more question, some of the research I am seeing indicates these low RPM readings may be due to a prop issue.
Yes, this is entirely possible. However, 14X13 is a very common prop on pontoons so I'd be very surprised if you're over propped. Please follow Racer's well-founded advice and do some basic troubleshooting before you start swapping parts.
A 2-stroke engine needs these things to run:
1) Fuel
2) Compression
3) Spark
Spark and compression are extremely easy and cheap to test.
Compression Test = $0
First, go to your local auto parts store and rent a compression gauge. Remove all spark plugs, make sure your battery is at full charge, and test each cylinder. You should see about 120PSI and less than 10% difference between all the cylinders. Return the gauge to the store and they'll refund your deposit.
Spark Test = $13
At the same store pick up a Lisle #50850 air gap spark tester. With the spark plugs still removed use the tool to test each individual spark plug lead. They should be able to jump a 7/16" gap with a clear blue flame.
If spark or compression fails on any cylinder stop and fix the problem. If all 4 holes are good then move to the next step which is spark plugs. Depending on the age spark plugs will foul and can result in poor performance like you're seeing. Get a fresh set of Champion QL82C plugs, gap them at 0.030" then retest the engine. If you're still limited in max RPM you then need to start tracking down the fuel system: carbs, filter, fuel pump, etc.
The thing is you've bought a 31 year old engine and you're relying on the seller (who was looking to make money) that the "engine ran good last year". You have no information on the service history, when plugs were changed, when the water pump was changed.....nothing. In these cases it's really the most safe option to assume none of that has been done and to install these routine service items before you go out and use the boat.
KJ