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Summary:
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EBC #MD1038-RS	$194
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CB 1		1989-1990

Galfer #DF059	$280
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CB 1		1989-1990
CB600 Hornet	1998-1999

Honda #45220KAF000ZA

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Research:
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http://cgi.ebay.com/ebaymotors/89-90-Honda-CB1-Galfer-front-brake-Wave-rotor_W0QQcmdZViewItemQQcategoryZ35592QQihZ022QQitemZ350054395006QQrdZ1QQsspagenameZWDVW
Galfer DF059 Front Rotor for 1989-90 Honda CB-1
Galfer uses the same rotor for the following:
CB 1		1989-1990
CB600 Hornet	1998-1999
Althoug, specs show the hornet with a 298mm rotor instead of 310mm.

http://www.bikebandit.com/product/10494?m=1962
EBC pro-lite front rotor #84313 for CB-1 $193.45

http://www.cmsnl.com/honda-cb400f-cb-1-us_model1010/partslist/F++10.html
Honda Part Number for fornt rotor is 45220KAF000ZA 
EBC X-Ref points to a 310mm MD1038-RS rotor for this part number


http://www.cb-1.com/frames/mcyclist.html 
310mm floating rotor and a dual-piston, single-action caliper
To the rear, a single-piston caliper works a 240mm disc.