Christian,
I have two copies of what Mike describes below:
besides 'mastered by capital' and 'KP'(Ken Perry mastered Palm Tree Lable), mine has matrix numbers of 'BSK-3010-F16'. the matrix number you want is the 'BSK-3010' part and then there are numrous codes for pressing runs.
you also want a textured cover, and heavy vinyl. if its a smooth cover or a thin pressing it's not early.
mikel
The exception is that mine are thin(ner) copies to me. They are probably the standard thickness of the day which was typically on the thin side during the late 70's.
One of my copies BSK-1-3010-F19 is a LA, California pressing. Sounds good
The other copy BSK-1-3010 WW2 F11 #4 is a Jacksonville, Illinois pressing. This one sounds significantly better.
Both pressings sound great played normally. However if you are able flip the phase in your Pass chain easily, it may fill in a bit more and add some solidity. I can easily hear this with my setup. This may be hit and miss as the system and speaker design may prefer one over the other or there may be not noticeable difference at all. That being said it may be worth a try. There is one last tip you could try quite easily with your Phantom if you are interested but it's a long shot and you may not see any value in it for this record. I'd try the phase flip first. I'm guessing your pass has a phase inversion switch somewhere in the chain. I didn't go looking for it so I'm not sure.
I don't have the 45's to compare but I can at least let you know that the standard first pressings are many and can sound different. From my perspective, it is no different from the shaded dog RCA's and which stamper you get...
Dre