OK, so I got as far as confirming the internal SCSI connector from a Duo 230 does indeed fit in the 2300c, implying as above that you could use a SCSI (and BlueSCSI v2) drive in it. See photo. I wish I could test it further but I couldn't get it to boot up...
My issue is, despite saying I...
Just yesterday I opened up my 2300c because it was struggling to boot (similar symptoms as yours). My mission was to remove the dead PRAM battery because I think I read that on these models a dead one can prevent boot and of course also leak causing corrosion. I did that, and it worked booted...