Yamatech, does the 1981 cb400t have the clevis to clevis shocks still? (if you don't know what that is it's a U shaped connector at both ends - go have a look it'll make sense)
If it does then you're lookin at slim pickins pal, stock length for a 78 cb400t (I own one) is a tad over 13"
I've found these to be the least expensive replacement option at $85:
http://www.partsnmore.com/parts/honda/cb400/?filters%5Bcategory%5D=chassis
about half way down the page they list 330mm clevis to clevis
Or try the guys at dimecitycycles.com they may be able to get a set for ya.
Good luck,
Devon 8)
edit: woohoo! this was my hundredth post