I'd say no. We all know that it's an engine with less miles on but there's still that nagging doubt that says if it's had a new engine then what else has/is going to go wrong? You'll lose about £1K off the value of the car I would imagine, and vastly limit the people who will buy the car. Given the choice of two cars, both identical except one has lower mileage but a replacement engine, most people (including me) would go for the one untouched.
sadly i know what he means, i went through this with a previous car. was a bugger to sell, ended up removing that information from the add. it wasn't a Cat C,D, A or B so no need to declare it. the car is in working order. but if asked during a sale about if the engine was replaced then you tell them exactly what work has been done. its down to the buyer to ask the right questions.
some people might think this a bit wrong, but if the car is well looked after, and the work is done by a reputable company with an engine that has a traceable history then the car is as good as new.
if selling on the forum and people now the history, then you also need to include it.