From mine experience, you can use the GVP HC8+ fully populated with 8Mb RAM and use it as the SCSI boot device controller.
GVP combos are slower than the dedicated SCSI controllers and 1Mb 30-pin SIMM are really cheap and easy to find.
Also, 16+8Mb is always better than just 16Mb (not the Amiga will really use this "huge" amount of RAM). RAM priority is automagically set, so if you have lumps of real-fast 32bit memory the slow Zorro-II memory will act just as a spare memory and DMA from the SCSI controller (will speed up the HC8+ SCSI).