You will need a set of thermos from an ef or el, a thermoswitch of some kind either electric or mechanical - Davies Craig sell these so does someone here on the forums. Also need 3 spst relays(40amp) 2 fusible links(40amp), Bunch of wire and connectors and some cable ties to make it neat again.
It all lined up very well for me but i have a six, but should be the same for the eight.
Instead of fusable links I used a circuit breaker, this way if I get a power spike from the fan jamming or being loaded up temporarily, the curcuit breaker will just switch off&on until the fault clears. Circuit breakers cost about $10 and are available at Supercheap ect and unlike links they dont "blow" permanently which is the last thing you want to happen when your stuck in traffic.
I use a 30 amp breaker because thats what most of the wiring in my car can take (more amps than this and the wiring acts as a fusable link ) . The twin thermos can spike to over 100 amps on startup so dont try to use a normal fuse as it wont last more than 1 or 2 startups. Once the fans are spinning they only draw about 16 amps.