if all original me pal says who is a vintage fender man says between £750 and £1500 dependent on overall condition. This includes playing.
Check it left the factory in natural, he has told me that it was the in thing in the 70s to sand down your strat, this can effect the price heavily.
I will get back to you with a resource for checking the serial number?
Also he said to make sure the neck pick up routing is as it should be, a lot of 70s strats had a hammer and chisel took to them in order to fit a DiMarzio humbucker. This again can effect the value.
Look at the join between the neck and the body for any gap. If there is this could be bad news. It is meant to be a common problem on fenders of that era.
Imagine if the words of Imagine ever came true.....