Mileage would never be my only deciding factor on a vehicle purchase. High mileage but well maintained will almost always be a safer bet over low miles and zero maintenance.
If I were looking at purchasing this vehicle my questions would be:
Why was the engine rebuilt, who rebuilt it, what parts exactly were replaced and what were they replaced with?
Finding out why it was in need of a rebuild may give you a better idea of how meticulous their maintenance habits were. Making sure it was a quality re-builder that used Toyota or better parts will tell you if the engine rebuild really is a positive or negative addition to the vehicle.
What else has been changed?
I know around 180k my 4Runner no longer felt like it once did. After around $800 worth of suspension components (some very needed others maybe not as much), it drove like new again. I wouldn't necessarily expect to have all of this type of stuff done, but if it isn't I would expect the price to reflect that. This holds true for fluid changes, tires, and any worn or damaged interior or exterior bits.
Good luck with purchase.