Trouble getting a slant six in the car

You need to shorten the chain on the hoist. Then you need to put a big screwdriver in one of the links in the chain on the engine that will hold it at a greater angle with the tail shaft point more down. That will help stab it in. SLOW and steady. This isn't sprint. It's a marathon. Slow and easy is how to not break anything or break you. You also need someone as a "spotter" to help make sure the tail shaft doesn't snag anything on the way in. Once you get it into the engine bay, use your floor jack under the tail shaft to get the angle more correct as you go in.