Most of the classic Mac OS line can be emulated a number of ways.

You'll need a Quadra 800 ROM file. You'll also need to create a PRAM file with the following command:

dd if=/dev/zero of=pram.img bs=256 count=1

Below is an example of the command needed to boot the System 7 installer:

qemu-system-m68k \
-M q800 \
-m 128 \
-bios Quadra800.rom \
-display gtk \
-g 800x600x8 \
-drive file=pram.img,format=raw,if=mtd \
-device scsi-cd,scsi-id=3,drive=cd0 \
-drive file=/path/to/system7.iso,format=raw,media=disk,if=none,id=cd0 \
-device scsi-hd,scsi-id=0,drive=hd0 \
-drive file=macintoshhd.img,format=raw,media=disk,if=none,id=hd0