Where am I leaking coolant???

[rhlanham]

Ok, I put a new waterpump and thermostat on my 84 C10 with the 4.1L six. While running, but way more noticeable as soon as I shut off the engine, I can hear what sounds like water boiling at the front of the engine block, and white steam is coming up (it does not appear to be smoke). I know my t-stat housing and hoses aren't leaking, so what should I check next? If it is a head gasket, would that be too difficult to replace for a weekend mechanic? I don't seem to understand this, because the truck was just leaking antifreeze, and not steaming/smoking. Now that I have put the new waterpump in, I get the steam/smoke. Any help would be greatly appreciated!! Thanks. Oh yeah, a question to make me look foolish - I forgot to see how the old t-stat was positioned, so when I installed the new one, I put it with longer side pointing down. Is this correct? Should I get a lower temp thermostat? Thanks again.