Originally Posted by Tjkeis
How do I found out the size of my gaskets? Do I take it into a mechanic shop because I don't know if my egine is original for my car size
If this is regarding the '65 American you posted about, don't do anything until you determine the condition of the vehicle. You said it was running bad- see if it needs a simple tune up before going deeper. With all due respect, tearing it apart at your skill level may mean the demise of the car altogether- a lot of well-intentioned guys have started out taking everything apart only to stall out because of the size of the job or lack of funds and/or knowledge.
The original engine can be determined by checking the VIN number; should be on the passenger side wheelwell under the hood. More here
There are various AMC/Rambler sites that may be of some help to you. Some general info is here