This has come up lots of times on AW and I read up on it when I bought my setup a little while back as came across a few people selling quattro springs used at decent prices.
The fronts are same, rear springs are different. The rears will most likely `fit` a FWD without any trouble as more or less same shape, but as the quattro springs are made for the extra weight of the indpendent suspension from what I know as the actual spring rate is different between the two.
Ie For stock oem springs quattro on the FWD rear will result in the car sitting higher then the front, and handling is likely to be affected too. Based on your sig showing ur new suspenson assumed thats what you meant?
If not and you have others then as aftermarket ones are stiffer by nature actual difference will depend on the spring manufacturer so may be turn out not too matter too much...
If aftermarket and your mate is gonna fit himself then ask him to try it and see how it turns out, if he`s gonna pay someone then might not be worth it. Oem won`t be worth trying from what I know.