Unfortunately, there are too many variables. Go to your local big box aviation store and see what they carry. It took me awhile to find solid compact blocks that were heavier. Standard cinder blocks were too bulky and light.
I actually don't know how much mine weigh. Those eight blocks can keep my io-540 and the nose wheel up in the air all day long. If you can find similar blocks, I don't think you'll have problems, even if you need to stack a few more.
Another option I've see is to get one of those large galvanized wash tubs, bolt it to the dolly, then fill it with some quick-crete. For about $50 you can make something the ACS sells for much more.