I am currently trying to buy a 280z with a 350 small block.  has a few problems. 
  
350 small block truck bottom 
64cc angle plug heads 
small cam  
aluminum intake 
carb 780 vacuum secondary 
  
turbo 400 stock 
  
stock 1976 280z auto rear diff (3.54) 
  
rear tires are 225/70/14 
  
apparently he saids the gear run out at 50?...he said is just the tires ....what could be reason behind this.  I really want this car, but i need to figure out what is making this problem occur. thanks