A tight head shot on 8x10 would be 1:1 magnifications. However the subject distance would be about the same. But it does give you the bellows draw needed. For a 600mm lens you would need 1200mm of bellows draw, and the subject distance would be, of course, 2.4 meters. Now you know why they did not do tight head shots on 8x10 or 11x14; but used a reducing back, usually the 4x5 back. After enlargers became generally available more options were available, but then they also used smaller cameras.