This is a really cool machine. I had to look it up and see pics first. Secondly, I am not sure of terminology but is the "finger" the part at 11:00 in the top photo? If so, with my 301 I had to remove the upper bobbin plate to free things up and be able to remove the bobbin case. I followed these directions
http://mysewingmachineobsession.blog...bbin-case.html I have no idea if this could help you, but am spit balling ideas here.
Also I have to remove the "jib screw" and it was horribly frozen. I soaked it well with Liquid Wrench, used a jewelers tiny screwdriver and a wrench to add torque. I was terrified I would strip it, but leaned into it and went slowly.