Would these spacers work on a 997 C4
 

http://www.ebay.com/itm/2pcs-brand-n...886eed&vxp=mtr

for the rear

you really want to use a 37mm spacer? MIght it work depending on your wheel, sure. Is it a good idea to me, no.

Also, these are cheap **** spacers that don't even offer a lip to hold the wheel on. almost guaranteed vibrations.

I would pass and get something reputable.

Hang a plumb line from your fender well and see how it would look if your wheels moved out another ~37mm/1.5"

I have 15mm on the rear of mine and would not go any wider