Sigh. Yes the install script would be in the standard edition of the 1989 version of 6.0.3, and every version of the System software thereafter. What I'm trying to say, but evidently not plainly enough, is that there may have been a customized Disk Tools that shipped only with the SE/30, which would not have had any installers on it. Like my Mac Plus disks, every disk may have been custom labeled SE/30, and possibly even included only the SE/30 installer, and not the installers for every other Mac.
Or, are you saying that the SE/30 is the only install script on your 6.0.3 disks?