Given a fixed distance of BK12 and BF12 blocks, what length should the SFU 1605 be?

Same question with SFU 2005 with BK15 and BF15 blocks, or in reverse, given standard machining, how far apart will the blocks be given a length of SFU2005?

Any Diagrams out there that show the placement of the blocks on the ballscrews?

Any help would be appreciated.