The mounting rings for L-500s will fit most guitars with regular humbuckers with no modifications. As the L-500 has narrower coils, the supplied rings will cover the small gap between the regular ring and the pickup. However, the L-500 will fit most regular rings, too if you can live with this little gap. In addition, the L-500 will fit P-90 routings, with the rings covering up the extra length.
The L-450 has got "standard" sized coils and will fit any humbucker ring except the 500-variety.