I've wondered what use they would be for wagon underframes, so taking already-used parts from the old i/c loco chassis, I had a play:
Top of the picture is a BlackDog 6ft chassis for comparison. The sample under that uses the Dapol suspension wrong way up without the spring, I think that this would pass quite well in O9.
The bottom sample uses the Dapol axlebox right way up and chopped about a little (lot) the idea is to fill up the gaps either side above the axlebox with filler, this would be more suited to O-16.5 or Gn15.
Oh well, kept me occupied for half an hour....