My pulley is fully scratch built. I originally had a full aluminium front pulley. But when I pulled that motor down, the pulley had split through the trough of the keyway. It was guite thin through there on account of there being a spedy sleeve over it to prevent the timing cover seal wearing the aluminium seal journal down.
On my current engine, the centre boss is all steel, with the crank pulley, and blower drive pulley being made of aluminium, and bolted to the boss. That make sense?

A mate of mine has a RWD 323 wagon running an S/C12 on 1400cc sohc motor. it did make 7psi on a 1:1 ratio. He then went to a 170mm drive pulley, (Blower pulley is 125mm) and the boost jumped to 13.5. But it was acompanyed by detonation. A simple water injection made from an old washer bottle running 50/50 water meths fixed it.