On Royal
I would start by draining oil first, there is a good chance there is water in it.
Once the oil is empty, just bump the starter a couple times to see if it is frozen or still free. Or pull the small round cover that is held on by 2 cross recess screws and use a 32mm socket to hand turn the engine. If it is frozen then odds are you need a whole new engine. If its not frozen then add oil and spin it up with the starter and no spark plugs just to get the oil circulating.
On standard
I would try to start it just to see where you are starting from. Even though the carbs were recently rebuilt, it was then allowed to sit and the carbs are likely gummed up. The gas that you will try starting it on should have a heavy dose of Seafoam, that will go a long way to cleaning out some gunk.
Start by draining the old gas out of the system. there is a drain screw on each carb that you can open to drain the float bowls. with those drains still open turn on the key and the fuel pump will run for about 2 seconds. You will need to cycle the power a few times to get all of the old gas out of the system and you new gas into the system. Close the carb drains and cycle power till you no longer hear the fuel pump clicking at power up. try to start it.
As for differences between the Standard and Royal.
As you already noted there is the CLASS air system, and the cassette deck. the standard does not have any audio system or intercom system at all. Many standards have after market audio systems added.
While the CLASS system is cool, it can only be adjusted with the engine turned off and the key in the Accy position. It is not very often that I have to adjust the air in my suspension and it only takes a minute with a small hand pump. The CLASS system is also a good source of headaches to keep it working between leaking seals and bad solder joints on the PC Board. All are easily fixable but just add one more thing to maintain.