you will get away with leaving the head on if the head gasket has,nt fused to the cover cookiesmicra, the cover has 2 locating dowels that make it hard not to scar the head gasket as you lever it off, and hammer it back on (iirc nissan sent a bulletin to the dealers to leave the dowels out on refit, when the k12 chain issues hit)
and yes sump off