Take an objective look at the load bearing walls, if any. In my previous home, the attic was good for storage. As the space went directly over a load bearing wall. Although all that went up there was lightweight holiday decorations and some boxes of packing materials from the move. I could have loaded that area up with 2000 pounds and not have stressed anything.
In my current house, I have (sort of) a "bonus room" over my 3 car garage. It has a specific weight rating. In both total load, and pounds per square feet. Nothing supports the floor from underneath. The roof trusses are designed to rest on the concrete walls, and the floor hangs down a few feet from the trusses. Literally, framework straight down from each truss, and 2x6's across provide the floor structure, in a "U" shape.
I'd be a fool to put diesel engine blocks up there. But it's a Dade County, hurricane rated truss setup, and is quite sturdy for it's 2000 pound rating.
Without knowing your configuration, also consider that it may be possible to use a "lally" column to improve the weight bearing capacity of your attic. I could do this in the middle of my garage, between both doors, and put my diesel engine block on top