OS9, right? Doug mentions some good things, but as long as you've got
serial numbers (and installers should you need 'em) you can do a
straight Finder-copy of everything.

I do it all the time to support 150 OS-9 macs in a publishing
environment. only a few things require the entry of a serial number
but nothing needs a re-install. Some pro audio apps and plug-in
packages might be different.

i say go for it. pop a new drive in there, copy it, remove the old,
reauthorize if you need to, fall back to your original drive if you
must.