I can't make out what it might have been, but the photos aren't clear either (hopefully your photos & not my eyes!). I see yours has the C4# present but without the HM9424-1#, whereas mine has the HM# but without the C4#. Also, mine was cast less any "call-out" or even a pad for such, and with the draft-tube/breather machining, perhaps an earlier unit?
Scott.
All casting versions and or how they were machined Holman-Moody with their bird logo through the COBRA lettered model included the Holman-Moody engineering number cast in. The Shelby number was added for COBRA versions; a casting configuration but final machining done more than one way.
The Holman-Moody number was dropped for the TIGER lettered version and the version with a long raised pad with rounded ends.
If you find one without the Holman Moody number cast into it, it was one of these last two versions.
To be clear these were sized for 260 c.i.d. engines in terms of what was considered a performance engine of the 1961-62 time frame. (Maybe that is why I have not come across a running engine with one of these (any version) is use.) In Cobra terms the 260 4V engines Ford supplied were in two known variants. (The 1963 Lola GTMK VIs used the Ford 260 4V race engines also.)
1) XHP-260 (Experimental High Performance 260), used 1962 model year oil pump pick up (modified for racing by Ford) and oil pan: Besides most fasteners and some ancillary pieces or assemblies most of the engine parts were unique to the racing experimental 260 engines Ford engineers built in house at great cost. Most of the individual parts had their own serial numbers and many parts were designs that never made it into any other known Ford engine. Not many were made, best information available to date makes me think that between 14 and 35 assemblies were made.
2) HP260 (High Performance 260), used 1963 model year oil pump pick up and oil pan (1962 and 1963 model year designs are different depths, mixing a 1962 pick up and a 1963 pan jams the oil intake against the floor of the oil pan which nearly cuts off oil flow.): This engine still used a lot of parts no other Ford engine did but it was almost production ready. Ford made at least 137 of them and probably more. The ignition distributor and camshaft of the HP289s coming out in early 1963 were very much like HP260 versions.
PS 260 c.i.d. engines for Sunbeam Tigers were not based on XHP-260 or HP260 engines.