This is from my buddy Steve at HondaTwins - so it's good info.
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In this post, I'll list KNOWN swaps for customizing....I'll add to the lists
as time allows.....
Forks: 35MM
Pre 79; SOHC CB750/4, SOHC CB650/4, CB550/4, CB500/4, pinch type CB450 &
CB500T.....
ANY matched pair from one of these bikes will fit the trees of any other of
these as tube to tube widths are the same.
"Top-Bolt" 450 forks fit only the original 450 trees (narrower) and SOME
CB/CL 72/77 (305) trees
Forks: 33MM
Early CX 500, CM series 400's/450's, CB/CL360 and "G" model 350's....
"Top-Bolt" 350 forks PROPERLY fit only "top-bolt" trees, but can be used in
later trees (they look "awkward" though)..
Disc-Brake wheels: The 450, 500T, 500/4, 550/4, and 750 disc WHEELS (6-bolt)
are the same and will swap....But rotor size varies, and usually must be
used with the bottom legs (sliders) of the bike it came from, or you can
swap the rotors or sliders.....
The CX 500 and CB 650, and post '77 750 5-bolt rotor wheels, both comstar
and spoked can be swapped, but sometimes requires the axle and spacers be
changed.
Trees: TOP...
CB 450, CB 500T, CB 650/4, and early CB750/4 tops all exchange.....The 750,
650 and 450 (500T) share the identical spacing AND offset (a non-cushioned
750 top tree will fit to a 450 bottom tree (stem and bracket) for those who
desire rigid handlebar mountings.( the 750 stem is longer.and only fits the
750) The cushioned 450 top tree will fit the 650 lower tree and forks if you
desire the "give"....
The 500/4 and 550/4 trees have less offset, but will fit the 450 , 360, or
350 neck ( if someone wants 35mm forks on their 350/360 cafe bike.)
Trees: Bike to bike: 360 trees (350G) will fit any 350, any 360, any CM 400
Variant, and the 450/500T, 500-550/4 and 650/4 necks
450 trees fit 450's and 500T and can be used as a pair on the 500-550/4's or
ANY 350, 360, CM 400, or CB 650
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