Thanks for the info about the 1/8" thinner dimension of that block. If you have a rough drawing I'd be interested in seeing it although your description is simple enough.
If you are asking about the rivet I was talking about, here is a photo I took of it. There is one rivet on each side of the subframe that holds the cowl assembly to the cab assembly after all of the cowl bolts are removed. This may be similar on your wagon, but I can't say for sure. It will probably be easiest to insert the block once the cowl is removed from the rest of the body. Someone more familiar with that body style would be able to say for sure.