Joshua Stein has made a very specific utility:
StuffIt is the de-facto standard for file archiving and compression on Mac OS before OS X. Most old Macintosh software is preserved in StuffIt format, but a breaking change in StuffIt 5 makes archives created in this version unreadable in older versions of StuffIt. Since StuffIt 3.5 is the last version that works on System 6, many archives cannot be opened on compact Macs running System 6.
ReStuff is a SaaS that automatically converts StuffIt version 4 & 5 archives to a format readable in StuffIt 3.
Go read how this works. I love it.