There are two well-known circuits well described in the Internet, including this site:
I want to combine them like shown below:
Will this schematic provide protection as expected, against overvoltage and reverse polarity?
Most likely, no. When the SCR fires on an overvoltage, the crowbar current that is needed to blow the fuse also passes through the FET. Since the FET's source is then dragged down to near the negative rail, it'll drop out of conduction, leaving the intrinsic diode passing that current, and it'll almost certainly pop before the fuse.
You could reverse the order of the two parts. Since you don't want the Zener in the crowbar to forward conduct on reverse connection, you'd need to add a diode below R1