You're correct in your inference about the b-pour getting between the part and the a-pour to cause those marks. This is half of the reason why we say to make sure that the parts are not dislodged from the a-half before the b-half is poured!
I don't think you'll be able to cast the hands without a little channel to each finger.They really aren't going to be easy. The hair I'm really concerned about. I can't think of any way it will be able to be done at room pressure so I think you're going to just have to experiment. You're really pushing the limits here.
Micro-bubbles are something we all forgot to mention. That's the biggest downside to room pressure casting. You're going to have to use a putty/filler and then sand it all smooth. Without using pressure and/or vacuum there is absolutely nothing that I know of you can do about them. Unfortunately I think we've come back to my initial comments at the start of this thread: you need at the very least to use pressure casting.
All these ideas about hacking up pressure vessels and hand pumps aren't worth the effort. Hand vacuum pumps are useless as you need to reach quite a significant vacuum to have the desired effect. Those pressure vessels aren't designed for continual opening and sealing and could actually end up being quite dangerous. If you're serious about casting (particularly these complicated pieces) then you need to buy a proper pressure pot and compressor. There is no other way. Keep searching around Europe for one a the right price. I've said it many times: anything but very basic casting should only be pursued if you have the time and money to invest in it.
Sorry to end the post on a negative note like that.
