[Kosan]

http://www.edesignaudio.com/6000s_spec.htm

Dimensions / Physical Information ( Eu-600 Midrange )

Mounting Depth 2.80" - ( 72 mm )
Mounting Diameter 5.60" - ( 143 mm)
Overall Diameter 6.75" - ( 172 mm )
Displacement .01cF -

Dimensions / Physical Information ( Eu-600 Tweeter )

Mounting Depth .60" - ( 16 mm )
Mounting Diameter 1.65" - ( 41 mm )
Overall Frontal Diameter 1.90" - ( 49 mm )

From what I read throughout this forum, some 6.5's fit and some dont. I prefer not to do any modifications.