The links jhm & calZ are great. For a street car what I have found is that if you strengthen the frame rails then do some basic strut bars the car is plenty stiff for your needs and if you want to a bit more then do some further bars just for the towers; this will avoid needing cage. If you do want to race you would just need a hoop but for street there is no need. I added some pics of my rails and others have done similar versions. I did another 240Z where we found great boxed rails that were thinner and fully boxed so we just welded that on the bottom and eliminated welding inside the car; easier and similar result. This way your car is more street and others driving with you will appreciate not being in a cage. I own a more caged Z as well but when you get older you will find women often do not want to be in a caged car, maybe just a hoop but nothing more...