I'm sure there are exceptions to everything, but all 292 cranks I have ever seen all have the larger flywheel bolts. So first, I would confirm the engine with the smaller bolts that you think is a 292 really is one. If it is a 292 but has the smaller bolt size, you can just drill and tap them to the larger size with little effort as long as the flange is thick enough around its perimeter to allow it.
Also, to verify if the block is US or Mexican, just look on the side of the block. It is cast into the side "Hecho en Mexico" if it is. I have also seen a few blocks made in Canada as well, and they have a little different type of casting symbol in the side of those blocks.
