Mk1 XR2 block is known as 771M , from US spec Fiesta. From what I remember, the Fiesta block doesn't have the engine mount holes for RWD application, and the old Escort 711M block doesn't have the holes for the Fiesta right hand engine mount. Not 100% sure on that though.
Found this Googling
I know the Haynes "Ford Fiesta 1976 - 1983 (#334)" covers the very similar crossflow block variant, the 771M (the Mk1 XR2's 1600 has no side engine mounts and a shortened water pump / timing chain/crank area which can't take a duplex timing chain), 'cos I've got one of them
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Valencia was the Fiesta engine 950,1100,1300 (modified Kent), then went to HCS in 1989 used in later Escorts and Fiestas, up to 1300cc.