shock length

[baz-r]

the main diffrence is (for std sierra shocks) cost and availble makes realy

a 13"-9" is a std coilover size but with an 1" extended top eye is not so you have to pay more and the makes availble are only protec or gaz from a few suppliers

if you use a 14"-9.5" unit its the next std coilover size up it has the correct open length without been extended and you can buy almost any make of coilover spax,avo,gaz,protec and so on so if you want a higher quaity make or want a cheaper option of the extended makes and you can buy from anywhere

you want to use a 1" longer spring in the rears than the extended type and orignal size in the front to have the spring seats mid way with the ride hight set correctly with 14-9.5's
also you need to trim a slighty larger hole in the side pannel to clear the spring