My cousin said he did one on a 12v, but i would think the pan would be a pain! I changed a oil pan gasket once when i had the tranny out of my 01, and it was not fun replacing the gasket with the tranny out either.
I say pull the engine but my cousin didnt act like it was a problem because ive ask him before about doing a n frame with the engine in the truck!
He never said much about the crossmember,
He just acted like he jacked the engine up.