Well I'm assuming this is for a S30, because that is the information I'll be providing.  
  
'75 280z  
49-1/2" side to side  
12-1/2"to 13" from windshield to face @ center of dash.  
10" from left side to c/of steering column  
7" from top of dash to opening of steering column  (top of clamshell) 
12-1/2"to 13" top of dash to bottom @ the center of dash