Dear Trevor,
Again thanks for your kind and helpful mail.
I had some minutes yesterday evening and found the guy you mentioned - thanks!
I also looked on the Internet for automatic gearboxes with OD like the one you described for the Singer, but did not find anything - perhaps, as you say, the best option is to try to source a BW35, perhaps from a Mk III Magnette, and take it from there. (I have also contacted local experts, who are looking into other options, i.a. an AW71 (user in many Volvos), but I am uncertain as to their verdict.)
Again, many thanks for your help.
Kind regards
Dag