What strut tower is recommend and that will fit my 2006 G35X if I install a plenum spacer?

 

Installing a plenum spacer will not affect your strut towers.

If you are running a strut tower bar, Motordyne supplies you with hardware to place over the top strut bolts to clear the spacer (either 5/16" or 1/2"... go with the 5/16").

 

I have an NRG strut tower brace that is adjustable in height so I just set it about 3/16" above my plenum.