I would pull the pan. It is cheaper and easier. You won't see the valves but you can see the cam. Look for 21A rods and the big clean outs for a Merc crank.
Coat hanger?? How the hell do you get a coathanger down the plug hole on a flathead? Look in there and you see a valve lookin back at you!! I'd pull the head before I pulled the pan unless, like you say, you may want to know whats in there. If it's on a stand why not do both.
The big cleanouts aren't a sure thing. A nearly foolproof way is to measure across the large counterweight - <6" = Ford 3-3/4" >6" = Merc 4" The 21A rods will indicate the journals were turned down to the early 1.999" size & while I don't know of many folks who would go to that trouble w/o offset grinding to get the increase in stroke, stranger things have happened...
Many cranks were cut to 21A size for circle track stock displacement uses, less weight, and probably some were cut to save damaged crank...just pull the damned head and stana ruler in there! Piston is likely normal dome with those heads, so is very likely to have info stamped on it too.
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