Welcome to the forum and congrats on your Monaco.
I don't have an answer for the engine size. If no one comes along with the answer, maybe you could try a Chrysler forum. Someone will know how to tell which engine you have in the Dodge.
If the brakes are working, that's great. Now, check the tires. Look for the age of the tires, it will be marked on the sidewall.
RV tires usually age out before they wear out. So, if the tires look good and have decent tread, they may still need to be replace because of their age.
A blowout can cause a lot of damage to a RV. Plus, there's the possibility of a crash.