As far as I remember you can use pretty much any SCSI CD ROM or CD writer drive in a Performa 630. Depending to the device and the system software version you might need to add additional driver software or slightly tweak the system software to enable operability with a non apple branded CD drive. Years ago I set up a Quadra 840AV with internal both a CD-ROM and a CD-Burner (after some chassis modification to mount two 5.25" drives). Both optical drives were non Apple branded and the system software was Mac OS 8.1. Both drives were very well usable, as intended, and at least one of them was bootable, as well. Mac OS 8.1 will run very well on a Performa 630 as long as a sound amount of RAM is present in the RAM slot(s). Details on required memory specification are given here:
Apple Memory Guide (page 22). In addition to this source you might note that more recent 72 pin SIMMs with up to 128 MB might work as well (60ns or 80ns, non parity type, no matter if FPM or EDO, support for
single-banked or
double-banked depends to the size (MBs) of the memory module and the actual mainboard and slot number used). Some of those SIMM are large and could interfere with the case on inserting the motherboard drawer. Better go for low profile types that will fit into other machines well, also. Those SIMMs are sometimes advertised as compatible with Amiga Blizzard computers and will fit nicely into the Performa 630.
More information on proper choice of memory modules for your machine is given here:
Quadra 605 Upgrades. Memory-wise the Quadra 605, Performa 475 and Performa 630 series computers appear to be mostly compatible. If you are annoyed from the extended cold boot duration of a Performa 630 with installed 128MB module, just disable the memory test (invoke the control panel »memory« with the Option-key depressed and tick the appropriate checkbox.