1. Get a USB flash drive. 
2. Flash the W8 ISO image to it.    
3. Physically install the SSD, do not remove the HDD.   
4. Set your BIOS/UEFI to boot into USB first then SSD second. 
5. Do a CLEAN installation of Windows 8 onto the empty SSD.   
6. You will find the previous installation/Windows 7 available as a mounted drive in My Computer. You can then ferry files and settings as you need to.   

Using the "upgrade" option is never a good idea, just a lazy one. Microsoft has worked extremely hard on upgrade but yet still it puts most software into an unknown state (i.e. beyond the software vendor's remit).   

If you do the above you will actually be able to boot into the "old" installation just by changing the BIOS/UEFI, so if you aren't able to figure out how to extract information just using drive access (e.g. the registry hives) then you can boot it per normal and just launch RegEdit.   

There is 0% information loss.   

PS - The same exact thing will work using DVDs instead of USB flash drives. Just write the ISO to a DVD.