Thanks Bob. If anything I would say based on what you sent me they are the straight frame ones. Either which way the Walther HO truck looks like a perfect match.
Another reason I would say the straight frame is the ticket is the description in your first link says that the older straight frame trucks were relegated to cabooses that were on branch lines, and considering how STMA came about at the demise of the Milwaukee it would make sense that they purchased a pair of older cabooses that were used for local service in and around St Maries Idaho. I am sure they just purchased the equipment that was already stationed there.
If I can’t get any more information on them, I always have the option of driving the 30 minutes to St Maries with a tape measure in hand and measure the darn ting.