HP blocks also had thicker bore castings
as for steel cranks, yes the earlier smaller engines 149,161,179 had nodular steel cranks, but i am pretty sure that the 202's from the XU1 GTR (GTR only) also had them (please correct me if i am wrong), spun by heavy duty rods. later models all had cast cranks, and the blue motors (2.85 and 3.3) got the fully counterbalanced cast crankshaft which had bigger big end journals than the red cranks, spun buy the famous starfire rods (the strongers factory holden rods). These rods where the only decent thing to come of that gutless little 4cyl boat anchor.
A value on a HP block would depend on it's condtion and who was buying it, a virgin block (std bore, std height and std tunnels) is prolly worth about $250 to the right buyer, the steel crank about $450 (again it is a STD/STD virgin with no bend or damage). and the matching high compression head another $300
Someone mentioned a HP cast 308 block? depending on it's engine number it is most likely a GTS bathurst monaro block.