I am not sure how the Windows 8 installer will interact with GRUB. I would
guess it will overwrite the MBR and load the Windows 8 boot system. If your hard drive has a Windows System Partition marked as active, it should go ahead and install, but I can't guarantee that.
If you wanted, you might use the
Bootsect.exe command to change the MBR back to Windows 7 so you system would boot directly to Windows. That would loose your Ubuntu boot, of course, but it would no longer require any Ubuntu involvement. You could then set up the drive the way you want, and make an image of that, in case something goes wrong. Then, you could always re-image your Windows 7 install.
Any chance of booting into Windows and using the snipping tool to take a picture of your Disk Management window. Attach using the paperclip on advanced replies.