[dsraven]

attach high up on the engine with at least one end, if you can, so the engine will always want to hang right side up. if you attach lower down it may want to flip over so the attachment points are the highest up and the weight hangs below that. think of it like an old metal bucket full of water with a bale wire handle. would you want the bale wire handle attached to the bottom of the bucket or closer to the top of the bucket. attached low down will allow the bucket to roll and dump water.
my go to would be a quick home made plate to bolt up where the thermostat housing goes, as many bolt holes on the engine area as possible to spread the load between bolts, and with a longer tang that sticks up above the surface so a chain can be attached there in the centerline of the engine. a quick cardboard pattern with an extra hole top centre to attach a clevis for the chain. make a plate from flat bar or whatever as then you don't need to cut anything with a torch to a specific pattern, just drill holes. it doesn't need to look pretty but remember you will use it again for install. a square piece of 1/4" plate would be great and could likely be sourced from a local welding or fab shop. with the front attached at the top of the engine things will want to stay right side up.
at the rear I would use another home made bracket made from flat bar with holes drilled to mount to the starter bolts and flat washers or short lengths of pipe to allow the nuts to tighten up and keep the bracket tight on the block. made with a long tab at the top and another hole drilled to attach the chain clevis. the other end of the rearward chain would attach to a couple of manifold bolts. here i would attach a separate short length of chain bolted on tight to the head with some manifold bolts but loose enough to allow the chain to turn a little. a big flat washer between the chain and the head surface to stop any marring of the surface on the head. span the load between a couple of bolts with the short length of chain and then attach the longer rearward chain, that connects to the starter side, to that short chain like you would attach it to a bracket that is attached there. then adjust the rear chain and the front chain so they attach to the spreader/lifter bar you have. no brackets required just a couple of clevises, so if the L brackets come off thats probably better. locate/attach the spreader/lifter between the front and rear of the engine remembering the rear is gonna be heavier due to the bell-housing. I have a slew of smaller clevises that I use for this stuff and they attach easily to the jackall beam that I use for the spreader/lifter bar. when done no chain should be allowed to slip through a clevis as that will allow change to happen in your set up. when the engine lifts off the mounts you will see if it is going to be rear or front heavy and then you can set it down and do the required adjustments at that time before you pick it up for real.
of course, removing some head bolts and screwing in some replacement bolts with lift eyes attached would be the cats meow. doing this requires the head to be torqued up after the engine is installed back into the truck again though because loosening head bolts is going to affect the integrity of the gasket.
just my 2 cents, there are lots of ways to get the job done, some sketchier than others.