well offset is how far in or out the mounting point is, dont think it has much to do with clearing the brakes but how far in or out the rim sits. FWD rims on a mustang would look horrid. The only time you would run into issues is when the mount gets so darn close to the brake it cant meet up with the rotor, in that case I see your point and FWD rims probably wont clear.
__________________ 2003 Cobra Vert (Redfire) #3938 of 5082 @ 05/27/2003
472rwhp/493rwtq -Modification List - Dyno Sheet 2012 Mustang 3.7L M6 (Kona Blue) 2011 Ford Edge Sport (Red Metallic)