On PC it would be possible to use the effects from Cubase LE/SE/SX in the 32 bit version of Cubase 8.5 with minimal issues. This would allow your old projects to sound mostly the same as before, but since you’re on Mac I guess you’re out of luck. If you could use the old plugins in modern Cubase, the biggest difference in sound would come from the channel EQ, which was massively upgraded in newer versions. It sounds very different from the one in the version you’re using so you would have to adjust that manually.
That said most old Cubase stock effects got huge upgrades in recent versions, so it might be worth it to redo your mixes from scratch to take advantage of them.