You could probably get by without changing anything, perhaps not elegant but functional. The second (and third?) digit of chain size is chain width*, originally in 1/8s. 530 is 3/8" wide, 520 is 1/4", 525 fits in the middle at 5/16". If you wanted to line it up precisely you would add 1/2 of the difference, 1/32" (0.031") as a spacer inside the sprocket. That, assuming that the factory got the engine, chassis & swingarm put together that closely. I will predict that your chain will never know you changed sprocket width.
* Disclaimer: I have no idea what the 8 in 428 chain size means!
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06 DR 650, Moose RS Holder, Handguards and Skidplate, ProTaper bars, Garmin 60CSx, Motech racks w/ 20mm Ammo cans, Renazco, TKCs summer/17" SM wheels winter 08 Scrambler, Conti Trail Attacks and BlackTiger Fork mod, 05 FSE 450, 03 KLR 250, 02 FXDX, 72 WR 250 (again), 72 SL 350 K2 (again), 72 TR6R, 06 XT 225