Because lengthening the downrod does ZERO for the pedal ratio. All that would do is reclock the Z-bar and cause you to have to shorten the adjuster link, and you would even lose ratio with that idea.
A stock SBM V8 clutch is a 10.5
TO bearing is same for all SBMs
Before you start on pulling that pedal out, make sure your fork is not hitting the bellhouse window at full pedal.