so I guess i'm looking for a 340 for my 69 dart

i'm going to start looking for 340 stuff to swap out my225
want it to look 100% oe but not worried about date codes or stuff like that
i guess 340 were made 68 to 72 is there any thing i should look for (72 better then 68 ect.)
not going anything crazy want it to idle nice /stock exhaust /stock air filter
are all the sb sub frames the same (or do i need only 69)
i know its a lot to ask but i do see on fb market place stuff coming up and if something is local i might jump on it
is there something to stay away from
i'll start read threw the forums
thanks paul