Lifting engine for installation
They will hold thousands of pounds.
http://www.kaizen-ms.com/Loadlevelingliftplate.html
These guys had one tested, and it held almost 8000 pounds. When it did go, it was the loop where the hook attaches that actually failed, not the carb studs.
If your hoist will do it, you could lift the whole front of the car off of the ground.
I pulled my iron headed 318 with aluminum LD4B intake and 904 attached with a carb plate (didn't have to pull the hood either), and that's far from the heaviest thing I've pulled with one.
EDIT: Just don't do it with one of those popcan chinese intakes on there! haha