You are going to have to make a choice about who you believe, and you are also going to have to start learning a new language if you plan to start decoding Ford part numbers.
@Broncobowsher is still giving you great advice. But ALL advice is context specific.
First, 6015 is not an engine assembly. 6015 is a block foundry casting root number. The prefix is C8OE, which is 1968 Intermediate Car. So don't stop at Fairlane and Torino. There are Mustangs, Falcons, and Cougars and a few Montego's in the intermediate platform.
7HIO = 7H10 = August 10, 1967 in your case. That is not the "Block Stamp" It is the Block casting number. The Block Stamp is located on the driver's side cylinder head deck, next to the timing cover. and it's stamped.
C8OE-6015-A the -A means the first major version or revision of this part. It is hugely important when you have multiple designs running concurrent in the engineering design workflow. The difference between an "A" and a "B" could be a V8-289, or a I6 200. It can be very important.
The C8OE-6015-A is a cylinder block cast in the Cleveland, OHIO foundry. It was NOT cast in the Windsor, Ontario, Canada foundry. The C8OE-A block is a 4 inch bore, 8.2 deck small block. It usually has the numbers "302" cast in the lifter galley. In 1967, and 1968, you could get a C8OE-A block in a 289, or a 302 depending on how it was built. So your C8OE-A, "302 Windsor Block" was available in a 1967 Ford Bronco (and Mustang) as a 2bbl, 289 engine from the Cleveland Engine Plant. Nothing to do with 1968, or Windsor, or a 302. (But it was an Engine Block.)
Yes, for certain parts, it is vastly easier to source parts for a 1968 Ford Mustang 289-2bbl, VIN-C. But this discussion is not remotely related to the timing chain. Every Ford small Block, (including 351W) from 1962 to 2004 uses the same 10.62 inch long timing chain with 58 links.