The pistons are dished as they should be. Flat ones were used in Holbay versions of the 1725 cc engine. The sump is steel as it should be. Alu sumps were standard on the first of the Fastback Rapiers, later on they went back to steel.
This is certainly no Rootes engine number! The only explanation I am able to come up with is that there is installed either an engine block produced in France and offered for several years by Greenwood in the UK or an engine(block) of an Iranian Peykan.