OK I have like well over fifty of these bricks and they vary a lot. Some have covered holes some not. The position of the holes varies depending generally on where they were made. The depths of the screws also vary and can be quite close to the surface where others are over an inch down. Screws can be flat or dome and can be quite small dome headed screws.
The unit is heavy because I assume it is full of resin. I guess you would have to hope that they didn't simply glue the unit together and blank off the holes.
There was also a brick for the 590 with the circular connector.
I have always used these heavy bricks on my expanded A1200 machines. I struggled back in 1995 fitting a 1GB 3.5" to a 1200 and found the only way was to use a heavy brick. I have bought busted broken 500s off Ebay at times just to get the bricks. I have been running set ups for like decades now I guess using the bricks. They have been a life saver.
scuzz
http://www.scuzzscink.com/amiga/a_amiga_inframe.htm