Yes, reseal teh pan before you drop it in.

I find dropping the front diff is the easiest way to go, you only have the 3 bolts holding the diff in place. This shoiuld give you enough room to get the pan out, thouigh I would recommend removing it completely, being able to install the pan directly from below will make it easier and less likely to scrape off the gasket material on install.

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed