I appreciate the follow-ups.
I've had a few ideas but thought I should post the question to see the responses.
Yes, I should contact SPCRR. They constructed a replica four wheel flat car called "Mary Jane". Based on the description it has wood bearings. I think they've had new journals boxes cast and recently had new wheels made for other car configurations.
The Colorado Railroad museum has the two bobber cabooses. Apparently D&RG caboose number 49 was converted back to four wheels. I've wondered if they used original or reproduction parts. Unfortunately, I don't get to Colorado as much as I used to.
Another source could be the H.K. Porter drawings since Porter made a number of four wheel tenders. I located a few tender drawings a while back but ran out of time looking for the journal box drawings.
James sent me photos of the standard gauge bobber caboose frame not too long ago. This would be ideal if it was smaller.
Before the end of the month I will have the opportunity to measure a number of bobber type narrow gauge cars although getting accurate internal dimensions of the journal boxes could be a challenge.
Regards...