930CK Head replacement question

I have a 1969 (I think) 930CK. I have a cracked head. I was able to aquire another head that looks almost identicle but the numbers are diff. Was doing some research to figure out what was diff. I found a listing that tells me this:

(My Orig Heads) #A33613 without decompression
(My New Head) #A20957 with decompression

What does this mean?
Can they be interchanged?
Can I mix-n-match (2 of one and 1 of another)
Which is better? A33613 or A20957

Thank you very much for any help

Bob

KevinT,
Trust me it wasnt hard to see the crack on this one. It looks like it froze and you could see bubbles when it was running. If in doubt you could take it to local speed shop and have them test it for cracks. I knew it was bad a year ago and searched Ebay and found me a rebuilt that some one was selling. Took me about 6 months to come across one. I paid $200 for it and looks like it was rebuilt too!! Sadly it was just a one shot deal. I did see on one web site you could buy a reman for around $400 plus core.

Hope that helps
Bob

So what makes it a "With Decompression" is the hole on the side of the head that some kind attachment makes the cyl decompress. The head and valves etc are the same. Correct?

Bob