That is an interesting car. From you photo it looks like a modified Series 2. It has a Series 2 roof and windows but Series 3 bumpers and door handles. Modifying it to fit those door handles would have taken time, skill and money. There are probably other modifications too - e.g the coolant expansion tank.
As others say, rust is the thing to be careful of but if that small spot is the worst then the car could be a good deal. Rust is expensive there on a Series 3 but less of a problem on the Series 2 (which this car is). Other main places to check for rust are door bottoms, floors, wheel arches and sills.
If you can maintain the car yourself, or know a good mechanic, then this could be a good buy but it will need more care and maintenance than a more modern car.