Best way to take out a slant 6?

Chains bolted to the head work fine; just use at least a grade 5 bolts; 2" is good, with a soft flat washer under the bolt head.

I bolted the chain between the 2 holes with some slack and moved the hook to near the front for engine alone; in that way, the load is partly carried on the 2nd bolt. The engine also hangs more stably that way. I also put a 2nd safety chain hooked on the engine; don't want a faulty bolt breaking and taking out my car or me. I have also bolted a lifting eye plate along the chain that is between the 2 head bolt holes to spread the load.

For the jack under the trannie, put a block of wood on it and lift the jack in place lightly BEFORE removing the trans x-member; there is a lot of weight on the trans mount, like 100-200 lbs. Once the hoist has the engine weight on it and you have lifted that 1/2" or so, then start to lower the jack. It is ideal if you can move the jack forward and lower it bit by bit as the engine is rasied and gets to the final lift angle.

You'll have to remove the rear U-joint to get the driveshaft out with the ball & trunnion so lift th rear anyway. It would be nigh impossible to properly re-torque all the B&T nuts back in place without turning the driveshaft.

BTW, I personally prefer to disconnect an auto trans and leave it in the car unless I am going to work on the trans at the same time as the engine. The auto trans disconnect is easy IMO, just make sure the torque converter does not pop out, and the trans front is jacked up or has a strap supporting it. You don't have to mess with the speedo, driveshaft, draining gobs of ATF, etc. Pulling off and re-installing an auto out of the car is no easier than in car IMO as they tend to be heavy.

For a manual, I remove the trans and leave the bell housing & clutch package in place, or pull the manual trans with the engine.