Finally found it! (was Re: Braided Steel Brake Lines on 92+ cars.)

[Jay Mitchell <jemitchell@compuserve.com>]

Duh,

I made the mistake of looking in the "Brakes" section of the rules for
allowance about brake lines. How stupid! The wording Richard quoted is
in the preamble to Section 13, and it was first put there in the 1993
rules. So, it IS legal to install braided brake and/or clutch flex hoses
on pre-1992 cars in Stock, and the reasoning parallels that of the other
allowances I mentioned.

Now, why the grandfathering remains there (and wrt steering wheels) but
not in engine allowances is another questions.

Jay