Install templates, set strike, and measure bore 

I receive such with suspicion and gratitude: both challenged to validate and reasonably tempted to move on.

I set my boring jig for hammer tails to bear on the stop and drill 1" from that stop for 1" tail lengths. All tails being the same means one setup for the whole set and setups take time. Also, tail wood vs hammer wool against the stop promotes accuracy. One tail length throughout also means all backchecks can be installed at the same height (2.5" in this case). Traditionally, Steinway tails had tapered lengths, longest in the bass, shortest in the high treble, and backchecks were installed accordingly, shortest in the bass, highest in the treble. The 1" tails may work with the original backchecks, but they will be challenged to reach in the bass, with excess overlap tail-to-backcheck in the treble. With the templates set at strike height and directly over hammer centers, bore (center to strike) can be measured directly. This requires a steady hand and good eyes. The alternative, which supports the calipers, is to measure from top of template to center. The template being 3" tall gives you the bore distance, plus 3". Bore distance plus tail length gives overall hammer length, which is what I want to cut my hammers to, providing I can purchase them longer than needed. I prefer blank, over-long tails that allow me plenty of room to cut where my measurements say I should. Steinway hammers are only available pre-cut to length, but fortunately they come slightly long or just right (in the middle) for the smaller models. Those with 20 bass hammers need a slightly shorter tails / taller backchecks in the bass or a slightly shorter bore distance to be consistent. I have done it both ways but feel the latter is simpler, retaining the one-setup-for-bore and the one-height-for-backcheck advantages. If I understand your example correctly, you get the basic format. No need to draw a bore line, however. That will come out right if your drawing, cutting, and boring setup are well done. The strike heights will almost certainly vary, highest in the middle, shortest at the ends. I therefore measure for bore length at the ends of each section, with an extra measurement in the middle of the long tenor section, to respect these differences. Custom boring in this fashion reduces compromise in the regulation and, more subtly, in the voicing.