How can I check to see if the oil passages are clear? When I put air in the single head oil passage, it only comes out one rocker bolt hole. On the crank, only when I put air into the oil filter hole, I only get air out of number three rod journal.

Oil passage in the head is a straight shot from the block to the rear most rocker shaft bolt. Oil gets to the rockers via the rocker shaft.
Block passages are too numerous to test from one single place.
Air only shows it isn't blocked, not that it is clear. Only true way to know is to wash them out with solvent and an engine cleaning brush. Or, run the appropriate sized drill bit through them.
Some great info here:
http://www.slantsix.org/forum/viewtopic.php?t=29492

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-MattMan
LEANED & MEAN

Thank you very much. I'll take a look.