This is from my "Engine Guide" on my website:
"ACCORDING TO FORD’S RECORDS OF DAILY PRODUCED ENGINES, THAT WERE ASSEMBLED BETWEEN JULY 9, 1928, (#236,787), AND OCTOBER 2, 1928, (#477,642), A NUMBER OF “SPECIAL EXPERIMENTAL” ENGINES WERE PRODUCED. THE RETURN OIL PIPE ASSEMBLY, A-6645, ALONG WITH THE OIL RETURN PIPE CONECTIONS ON THE BLOCK, A-6015, AND VALVE COVER CHAMBER, A-6520, WERE ALL DELETED. THE ADDITION OF OIL RETURN HOLES WERE DRILLED ON THE FLOOR OF THE VALVE CHAMBER TO ALLOW THE OIL TO DRAIN BACK INTO THE OIL PAN. EACH ENGINE HAD THE REGULAR MODEL A ENGINE NUMBER STAMPING TO INDICATE 1928 PRODUCTION. BETWEEN 1353 AND 1355 ENGINES OF THIS TYPE WERE BUILT. THESE CAN BE SUBSTANUATED BY THE “RELEASE” DATA OF APRIL 23, 1928 FOR EACH SPECIFIC PART AND THOSE FEW WHICH HAVE BEEN DOCUMENTED TODAY. ONE ENGINE NUMBER WHICH HAS BEEN DOCUMENTED SO FAR IS #286,625 (JULY 29, 1928). I AM SURE THERE ARE LOTS OF OTHERS".