I've never had a problem just removing the hood. If you are using something like an engine leveler, you may run into your hoist not having enough lift height. If not, just keep the chain reasonably short. As long as the transmission is disconnected you should be able to lift straight up.
Others probably know the best lifting points for the Chevy L6. I found some Ford FE engine lift brackets perfect match bolt holes on the top of the Pontiac head to lift with. Maybe the Chevy 250 has the same bolt spacing? Worse case, bolt a chain at the front, cross over and bolt somewhere on the rear. Then if it starts to tilt add a ratchet strap from one of the motor mount points (bolt the hook to the block or hook the mount) to the hoist hook and straighten it out.
The scariest point of any engine lift! And you don't have a nose to worry about! Anyways, you can see how I have the chain crossed over the top. Front left to rear right. Any 3/8th bolt hole will do. I am using two 5/16th holes holding the brackets on each end of the chain (think like a carb plate on a V8, way more than adequate).
