I have also just installed my fiamma bike rack but only got the 2 bike one at the moment , am sure there is wee grommets in place for the 3rd rail that sit in-between the 1st and 2nd rail and just bolt on , unfortunately I haven't looked at were the 4th rail goes but am assuming you bolt a bracket to under the 3rd rail via the four nuts that are already there or do they give you mibi longer bolts to replace the old ones with as that would make more sense , also my M8 has the T4 version and he says it's better to mount adjust the rails in a straddle position to mount the 4 bikes as to stop peddels getn in the way so for example rail one positioned to the left slightly , rail 2 to the right and 3rd to the left and 4th to right , am sure there is a diagram in the manual showing this , good luck with the build , I struggled building just the 2 as a feel the instructions weren't great if am honest and if you can get someone to help ye mount it then ad definitely take the help as I nearly dropped mine a few times trying to mount it to the top of tail gate as it's a bit tricky to get it in place correctly
