old Yamaha speedos and speedo drives - HELP

[Badcat]

hey all.
i have a "situation" and need some help.
my street tracker has:
an SR500 yamaha speedo (that is expecting an 18" front wheel)
a 19" front wheel
a speedo drive from an enduro bike with a 21' front wheel.
i haven't got a cable for it yet - but i assume it will be pretty innacurate..
so:
does anyone know whether all yamaha speedos are the same calibration wise?
because if they are - perhaps if i get a speedo drive from say an XJ750 (has a 19' Front wheel i think) my speedo would be close to accurate?
or should i just junk it and get a panoram?
any help or comment appreciated..
ken

[FROSTY:Me]

Ken-- a speedo is a speedo is a speedo--itll take the info its given and turn it to a reading. SOO the way to change things --Yup tis the speedo drive.
Ya dont have to be so narrow in ya search though matey.
If ya want to stick to yamaha -try XV750,850,1000 -xj550 and 650. XS 650,750,1100
TX750. RD250.350 400 and of course the mighty sr500
-If nothing fits they ya can bolt the whole plot together and get the speedo calibrated to what you've got.