Question about the"elevator" bolt being a flat head? Unlike the carriage head being semi-spherical/half some shape (what I'm familiar with) is the "elevator" bolt really flat headed? If so I wouldn't mind finding some of those!The "Lee" base blocks are pre-drilled to universally fit all "Lee" brand presses, but can be drilled to fit any press. The only requirement is that to use them you'll need some 'elevator' bolts (flat heads with a square shoulder) sort of like a 'carriage' bolt to bolt the press down. And you only need the 'base' block, not both pieces.
Another option is to cut your own 'base' block out of 1/2" plywood in the same pattern as the "Lee" base block. That way you can use most any bolt by simply counter boring the bottom side of the hole to hide the bolt head and retain a smooth base. You will also need to drill one 'locator' hole if you decide to use the plywood. I think you'll find a drawing in the box your bench block and base block set came in that describes how to cut the plywood. If not there, it can be 'Googled' I'm sure.