It's like a brace.tsegeela said:
If you look between the starter and the engine block, you'll see a length of metal that bolts into the engine block at the top end and the transmission at the bottom. I always found it easier to remove the starter to get at the upper bolt (on the block).
A little more info assuming this is a 318 or 360. I have done this twice on 2 different trucks. I ran into problems on my first time because the motor mounts were worn and I had a hard time to get the oil pan back up because of the cross member. I had to turn the crankshaft by hand (using the bolt at the front of the engine) to get the counter weights out of the way so the oil pan would go up. I also screwed up the oil pan gasket and had to drop it again and do it right.
Watch out when you are scraping the old gasket surface. The front 2 bolts go into the timing chain cover and that's aluminum (softer than the block).
Good luck and there's a lot of knowledge here to help you if you get stuck. The first time I did it I had to come in the house and login in here to ask questions.
Ted