Greg there should be a casting number on the side of the block. A C4AE-6015-A type of number like the head. It could be a C5,C6,C7 or C8 or similar as well. 66-427 was fairly generic and is on lots of FE blocks besides the 427. 53 is the mold number and DIF means Dearborn Iron Foundry. The 352 was the series number. If there is no casting number and it has vertical ribs on the side good chance it a service block. Same for the head number. There should be a letter after the 6090 like F for the 427 head in 64. Get the block date code under the oil filter adapter pad and post it. If the first number has two dots underneath it's a 70's service block. If no dots a regular production block date code. The date code for the heads is above the number you posted under the valve cover area. It will be a number/letter/number('s) G.