Hm. Regarding those Gazelle frame numbers: is there some public data base available? I only read about this one here:
http://www.rijwiel.net/dbase_n.htm
But there is no searchable data base available. I send an email to Herbert Kuner as stated in the text (no answer yet).
There must be some contemporary catalogues, leaflets etc, where we could compare the different manufacturers models with ours, I suppose. The cargo hold frame of ours is a bit special (though not unique, as it seems from the Pannerden-bakfiets) and should be to be identified.
The bakfiets is right now at Gerhards flat, we will meet tomorrow again and doubble-check the left saddle tube side for an additional number. We will dismantle the cranks then as well, so good time to measure the bottom bracket/axle/crank combo.