Creaking is usually metal on metal
Looking at the pic in Z1’s listing:
https://www.z1motorsports.com/suspen...QaAiNBEALw_wcB
Looks like it has an aluminum upper perch for the rear spring; because they are progressive instead of linear the diameter is different. Never seen thrust washers on a progressive spring but offhand I can’t think why it won’t work
I suggest calling SPL parts. They sell kw and swift and can figure it out