RE: Do You have a better idea about cowl mounting blocks?
Holy Cow! That's a lot of work!
I stick them right to the firewall with epoxy, no surface prep. Add a drop of Med CA with kicker to hold it in place until the epoxy cures. That's it! Never had one come loose even on big gassers.
Next, enlarge the screw hole, and fill it with a short piece of inner Nyrod. It will accept a #2 screw, and no more screws splitting the block (The nyrod can also be drilled out slightly to accept a #4 screw).