Disassembling Voigtlander Apo-Skopar process barrel lens

[Nodda Duma]

A photographer sent me a Voigtlander Apo-Skopar 45cm f/9 process lens that needs balsam separation repaired.

Rear group unscrews just fine, but I cannot get the front group disassembled. Does anybody have experience with this lens and knows where exactly the front group unscrews? I *think* it is the very front, in front of the threads as shown, but no matter what I try it --heat/cold, heat on the barrel / freeze the front, PB Blaster, etc. etc. it does not come undone.

Anybody have experience disassembling one of these? There was a series of them, different focal lengths.

here's a pic of the stubborn lens.