I do it the following way:
1. cables free at drum ends, everything free at handbrake lever, rod disconnected.
2. outer casing ferrules pushed all the way in, on both brake backplates and part #15. Tapping with a drift usually necessary.
3. fit part #22 in place, fit one cable end in it, then the other, then bend down its ends with pliers.
4. fit drum side cable ends to brake shoe levers. A little harder now that the other ends are not free, but way easier than doing it the opposite way.
5. fit brake shoes correctly ensuring the handbrake distance piece is slotted correctly.
6. pull back part #18 in order to align its hole with the first hole of the lever. A little levering with a screwdriver may be needed. Insert pin from top and don't bother with the split pin, it's impossible for the pin to come off.
7. engage rod on lever and first hole on ratchet lever.
8. adjust brake shoes as usual.
9. check handbrake travel, if excessive move rod one hole up at a time on the ratchet lever. When you reach the last hole and need shorter travel, reset the rod on the first hole, move part #18 one hole up in the lever and start over again.
P.S. Conratulations on the paint job, I admire better-than-professional paint jobs performed by amateurs!