Think the car is last driven by Mike Evans and i remember he was bloody fast with it. You could ask him for the history.
Why are you selling that engine? I would race the car with that engine before thinking of another, especialy more power. Think it stil has a 3rail gearbox and BMC axle, not ideal for Proto power i think.
You could also call Paul Freeman, he's the K1600 engine builder.
I remember prices around GBP 1500 (including dry sump and ecu) few years ago but not many sold last years as they last and last in K1600 form.
But again i wouldn't sell it if i were you.