Pre 73 won't be a defender it will either be a series 3 or 2, Defenders started circa 1985, genuine 70's cars will be leaf sprung, if it's on coil springs then be suspicious.
What you need to watch for is folk selling a pre 73 that they allege is on a range rover chassis, but is actually an 80's or 90's defender masquerading as a pre 73 for tax purposes, these are essentially ringers, ebay is full of them.
That doesn't put some folk off though