[Jac Mac]

The heads in pics posted by Mark do not have provision for the two extra cyl head bolts per cyl that the Indy 260 alloy block was cast with, so these should/must be another alloy block casting based on the factory 260 block if these engines were as you describe.
Note also the cresent shaped coolant transfer passage which also suggests the block would be based on early production 260 ford block as IIRC the Indy car blocks were dry decked with circular (O-Ring) for coolant transfer.