One shows RA#2 having a direct(not via FCC b)input interface with AT CMPTR.
Effectivity is:
GEF 002, 003, 006, 007, 009, 011, 012, 028, 030, 301-305, 309-399, 713, 714, 717, 719, 721-726, 728, 729, 733, 735, 737, 805, 810, 811, 817, 821, 826-829, 833, 834, 837, 839, 840, 843,848, 859-861; GEF 812, 825 POST SB 737-34-1758; GEF 815 POST SB 737-34-1941
That is the old (Smiths Autothrottle) install which has had both radio altimeters wired to it since inception on the first NG.
On the diagrams where you see with the #2 Rad Alt going to the right FCC, the next item to the right should not be the authrottle computer, it should say FCC-A underneath it as that's the Collins setup.
The SB's noted are for installation of the second FMC, so that's the change for GEF 812, 825 and 815.
What we've know is that the Smiths Autothrottle computer has both radio alitimeters wired to it. What we don't know is how the software inside uses the right radio altimeter input. I am still looking for absolute confirmation that my opinion is that the A/T computer looks at the left until it sends out NCD (Fail) and then switches to the right is correct.