I need some information please.
 

I am the owner of a 1971 Jeep CJ5 that was built for extreme off roading. The builder of my Jeep installed a big block Buick for power but I have no idea what size. I have looked between the plugs by the exhaust for casting numbers but can find any on either side. I do know that its a big block because of the aftermarket intake number. The plugs that are in it reference back to a 68-69 430 or a 70-74 455. so what I am looking for is,
1. How to determine which engine I have (I did see that only the bore is different so I'm assuming its the same block), and
2. What this engine needs to be timed at?
Any information would be more than I have now and would be greatly appreciated so i can get it running correctly. My email is pyat@hotmail.com. Feel free to mail me. Thank you.