Here is a great resource for SE/30 symptom troubleshooting. http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html
One thing, the scsi ID #7 should be showing up as the mac itself.
Been a while but ever do I remember the not so fun task of playing with SCSI voodoo.... All that said is to encourage you. Everybody that had external devices on those systems had issues from time to time.
An ID should be as below:
0: Internal HDD
7: Logic board
(this give you SCSI ID's 1-6 to set your external devices to)
While it is hard for me to diagnose from a distance, the first thing that I think is a clue is what you said about the hard drive working in the CD-ROM. Typically those old enclosures had their own SCSI ID selectors and that may be why the drive worked in the enclosure but not out of the enclosure. I think U still have SCSI ID conflicts; be very methodical. Choose one device, and work with it and the SE-30 till both boot together smoothly. Follow the advice from the link below.
If you continue having problems try running disk repair to see if disk boot data corruption may have occurred.
If the disk driver can be reloaded in Disk drive setup try that also.
Additionally, although not always reliable, try booting these devices after the Mac is up and running; they may not mount but SCSI Probe will see the device and what ID its occupying. This helps rule out the working devices from the suspect devices.
One last thought: make sure all cables and pins are clean, undamaged and fully connected before starting any equipment up. If there is even a chance a cable could be bad, get another known good cable to test if the same results occur or if this corrects the issue. Best regards.
Excellent! Glad to hear you were able to resolve it this way. It's one those issues that can result in headaches but once the Hard Disk Driver is reloaded these issues clears up sometimes.
Thanks for the mention and photos of SCSI Probe utility software; this or a similar utility are a must have when dealing with SCSI issues. Thanks for the update and how it all got resolved. Enjoy that SE-30; they have such a charm about them.