which head unit adapter are you talking about? ouch 100 bonez?

 

what do you mean by spacers? what speakers are you going to use?

 

spacers to allow for either different size speakers(depending on what's in there now).
http://cgi.ebay.com/2003-2004-INFINITI-G35-STEREO-DASH-KIT-COMBO-99-7604_W0QQitemZ130227550152QQihZ003QQcategoryZ85806QQrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247that's one of the more reasonable ones, 200 gets you most of the wiring you'll need.