If I am not mistaken, the pumps are the same, hubs the same, pulleys and brackets different between the 500EFI and 525EFI. The 500EFI matches the 575SCI ones. I am guessing the closed cooling system and/or different heads on the 525EFI comprise the need for different brackets and offset on the pulley. Hope this helps, someone else chime in if I am incorrect. You can also reference part numbers from many websites like mercruiserparts.com for example.
If you want to save some cash you can go to an auto parts store and get a PS pump... I did a bunch of online looking/comparing and ended up getting one at Advance Auto parts for $54.99 without a core. Pn for it is SP16070 ...other parts stores have these just different numbers, but it crosses back to a mid 80's Cadillac car. This is how I crossed back to a 849906A28 Merc pump. It is NOT the old saganaw style pump.