Welcome to our little world here. The first thing is it is unlikely you will get a great deal of assistance with this as we as a group tend to not like offering advice in things where people can stand under and be crushed or killed if it fails. Your insurance company would instantly abandon you if someone go hurt. Therefore our standard answer is, "get a qualified Engineer to design it for you."
Having said that, the risk is in your court and you have been warned, but there are beam calculators on this website that would provide figures that might be acceptable. A standard SWL (Safe Working Load) is generally accepted as 2.5-times the maximum working load. BUT, you do not yet know the actual load.
Posit, you are removing a truck engine and forgot to undo one bolt on the mounts. The lift begins and in a very short time, the truck is being requested to leave the ground along with the engine. Suddenly the 600-lb is not looking so good.
The bare beams should not rest on the wall, they should have footing plates to spread the load. The vertical edge of a concrete block will not carry a lot of compressive point-load. The beam needs to be secure from tipping to the side. A 5-degree twist in the beam can reduce its working load by as much as 40-percent. Suddenly that 600-lb now looks like 840-lb and well beyond the SWL you have envisaged.
So, at your risk you take advice from me. Personally, I would be walking the yellow pages for local Engineers. Too many things you are not aware of and thus not considering.
Finally, as an Engineer willing to take those risks with my own design for my own workshop, I have found over the years that a sturdy cherry-picker hoist far surpasses a fixed beam design. I have a 2-ton folding hoist and it has lifted everything from car and truck engines to a 3000lb lathe.