Stewart,
I was leaning towards that as a possibility after looking over photos of the locomotives for this line.
Jim and Jim,
It does seem likely that it is truss rod related and I hadn't considered that this type of block might be used up at the bolster.
The weather was perfect this weekend for treking out along the Magma AZ. We did see some white powder up in the mountains above Superior from the last storm that blew through to remind us that it really is winter.
Dave