Welcome. Its kinda 6 of one, half dozen of another-if you leave the trans in, no huge fluid loss+underneath time is minimum-no unbolting of crossmember-but the bellhousing bolts are a bear(somewhat easier w/a long box end 9/16)to get to. You'll need a jack under the trans. Pulling both is obviously heavier. Lining the engine back up to the trans in the truck when replacing it can be a pain, with both engine/trans together its easier to put into place in the frame . Either way the heater box needs pulled to make room.
