Or, look at the several, small raised sections on the block just under the spark plugs front and rear - they're called "bosses" - and see if one has a number stamped into it. Then let me know what that number is, and if it came out of a Cobra beyond the early cars maybe it can be identified.
If you don't recognize what Ned means, each side of the block will have two partially machined protrusions near the deck surfaces; that is a boss near all four corners. These tooling bosses were used to support blocks during some of the production processes.
Most HP289s in Cobras were five bolt models that carried Ford issued serial numbers for the blocks
(not the engines, reference Mr. Mannel’s research on HP289s, blocks were numbered before being used in engine assemblies) on their left side. The front left boss got two letter characters and the rear left boss got a sequential number up to four numeric characters long. There were thousands of Ford serialized five bolt HP289 blocks; numbers got up into the mid six thousand territory. (In round numbers only about 7 to 8% of the Ford serialized five bolt HP289 blocks made were installed in new Cobras at most. That does not count those they used up in race cars or sold retail.) The numeric part of the number was also typically hand painted on the rear of the block by Ford. SAI adopted this number as the engine number
. The ancillary chassis identification tags (what you would call warrantee plates on American cars) on CSX2201 and later cars had a place for an engine number
. SAI installers were not consistent in their stamping of ‘engine numbers’ into what Cobra owners call ‘foot box tags’. Sometimes they stamped the entire number, alpha and numeric characters, and sometimes they only stamped in the numeric characters.
There were exceptions. At least sixty one engines (based on examples known right now) acquired from Ford assembled in late August 1964 or later were different than all those that came before them. All known engines, except one, in cars with manual transmissions were five bolt engines built to different specifications than earlier engines. All the engines in cars that originally got C4 automatic transmissions that I know about came with six bolt HP289 engines that were themselves different that what Mustangs recieved. These late engines headed to SAI instead of a Ford vehicle assembly plant did not have Ford engine block serial numbers. (Ford did not serialize six bolt HP289 blocks before the engines were assembled, reference Mr.Mannel again.) These late engines received SAI assigned engine numbers
. These SAI engine numbers were stamped on the left rear tooling bosses and on foot box tags of Cobras they went into.