i worked for sony doing laptop repair for 5 years and i still do not understand their part numbers.
the A number that you have listed is going to be a series number meaning that you can get a board for any of the SZ400 series and they will all work. the bad news is if you do not get a SZ480 board when you try to restore the computer if will say you have the incorrect restore disks (even if the board is the SZ481 doesnt matter wrong restores) to get the exact SZ480 board you need the B number (which i will list at the bottom) and that will get you the exact same board for the SZ480. if you do not care about the restore disks working you can use any SZ400 series board if that is the case there are probably 20-30 different part numbers you have use.
here are some other part numbers to try
A-1253-322-A B-9986-047-2 B-9986-047-3
Ebay is full of other A part numbers (A1171213A is very common) that are around $100-130 and they all list another type of part number like MBX-147 (or 140, etc..). Is there any way of knowing whether any MBX-147 (regardless of the A part number) would work?
At this point, I'm still looking for a new laptop for myself, but this machine would work fine for the fiance and would be best if it worked properly.