The 77313-101-40LF: Both rows are fully populated (all 40 positions loaded), so the board layout is a straightforward 2×20 pattern with 0.100" row spacing. This is common for breakaway headers where you snap off the exact pin count needed, though this part ships as a fixed 40-position piece.
The tin-plated solder tails (78.7 µinch) are standard for through-hole soldering.
If your BOM needs more I/O on the same footprint grid, the 60-position version is a direct swap in terms of mating interface and board layout, just wider.