Look at the angle of the windscreen.
The hard top E type has a taller,steeper windscreen compared to the convertible. This will give you an idea of how well it's been done. If you've a hard top windscreen it's likely to be a poor quality hack off.
Compare
http://www.dyna.co.za...eries_1_Red_ss011.jpg
to
http://www.knowledger...etype.1966.750pix.jpg
Also note panic button's point about insurance and the fact that it will be difficult to sell on.
You haven't said what series or age it is - the really early one were awful - to such an extent that you'll see people advertising them as "series one and a half" to distinguish them from the first ones.
The story goes that after so many complaints Lofty England told one customer "I'm sorry sir we just sold you the engine - we gave you the car to take it home in"
But most importantly if you're about to buy an E-type you need an engineer or garage that is experienced in working on them. Over time you will need things fixed and you don't want to be taking it down to "Bill's corner garage"
Check the owners club for people in your area and give them a call and talk to them