not sure if you got this mounted or not but it does not attach to the firewall. the brace itself mounts to the strut towers on either side of the bearing caps. Basically you do need to drill holes to put the silver nut-serts in, and then it attaches to them. Did you get directions and don't understand, or did you not get directions?
It is still good. If you really want to use it I would call ABD and see if they can sell you just the mounting hardware kit. FYI : it will not really want to be a kit you want to tackle by yourself unless you have patience and time. It will mount to the top of the strut towers and you will need to cut holes in the top black metal shield.