With such an old engine I would not trust a 'running' engine without a complete strip and rebuild by somebody who really knows what they are doing and that can be expensive, roughly twice the cost of a 4 cylinder engine.
The cams are very prone to wear, even on low milage cosseted engines, my current engine is the first engine I have ever seen where the cam was good. I have had at least 8 Rover V8 cars inc. an MGB V8 which started popping back through the carbs because the cam lobes were worn away completely @ about 40,000 miles.
Great engine but you need to know what you are doing. The head and block faces are very easily damaged. I paid £150 for an SD1 engine and LT77 box recently at my local breakers, so they are out there.