Question about x's and o heads

[AARCUDADEN]

Okay guys need to know if x heads and o heads are compatible with one another. Reason i'm asking is i found a complete 69 340 a guy has for sale. Everything is there minus carb and exh. manifolds. Been sitting for many years covered up and all openings sealed tight. I want this engine simply for a back up in case i ever need one or a possible stoker for my Dart. I noticed one head is an x head and the other is an o head so that tells me sometime someone puked a head. This guy wants 1500 bucks for this engine and i know that's way too high so i'll make him an offer but i don't want to pay good money for an engine that has lets say a 318 head on it. 

[Chryco Psycho]

they have a different casting number but are essentially the same head as long as th O head has the 2.02 valves , I believe the last year of that casting did not .

[teslasbrain]

FYI, 1970 was actually a transition year and some engines came from the factory with mismatched heads,  having one X and one O, or one X and one J etc.  What are the date codes on the block and heads?