The 428 in my 59 is one of those ribbed service blocks, with no rear bulkhead scratch, but as mentioned, it does have the triple webbing. Although it does not have a "C" scratch on the rear bulkhead, it had a yellow "C" , in yellow paint there, or at least did until the block was hot tanked over the winter. I bought the engine about 35 years ago, from a guy that had bought it in the mid 70s as an over the counter 428 Cobra Jet short block, and he gave me the Ford warranty card with it. I just had the engine laying around the shop for almost 30 years before I did anything with it, and when I tore it down, it had 1973 dated "DAB" crank bearings throughout, big bolt C7AE-B rods, which had 5/8" rod nuts, rather than the oddball 19/32" nuts all my regular production CJ rods had, standard bore pistons, with "428 Super" cast around the pin bosses, and a "1UB" crankshaft. It also had the 428 cast into the bottom of the water jacket, not between the center core plug holes, but rather visible thru the long slot at the rear of the deck surface. The 428 number was only really readable on one side, on the other side, it was hard to tell, as the engine had been installed in a PU truck for years, and had a lot of rusty scale and sediment in the water jackets. About 6 years ago, I did a ball hone on the block, and just put new rings on the original 428 Super pistons, had the crank ground .010 and dynoed it with a small Oregon Cam solid flat tappet cam, which I posted on the dyno results page, under "near stock 428 CJ". After it hurt #8 rod bearing shortly before last years FE Reunion, I did a proper rebuild, including having the block sonic checked before having it bored .030", and the cylinder walls were all in the .175-.200" thickness range, at standard. I also did the drill bit test, and although I would have to look for the numbers, I seem to recall that they were all pretty narrow. I only have about 500-600 miles since the last build, and it runs great, with no issues of running hot. So if the OP has a similar block, he should be fine. I will have to double check, but I seem to recall the block casting date was for 1973, and it does have the triangle shaped water holes in the deck, but I have had several later triple web 360/390 "105" ribbed blocks, that also have the triangle water holes, so that alone is not definitive.