The non-professional engine re-build is not likely to command any price premium to a typical Boxster buyer.
With that being said, here is my suggestion if you want to sell the car for the most possible:
The extremely low miles
are a huge selling point. I'd target various Porsche forums and Porsche car clubs using the low miles to get potential buyers interested and to justify a higher than Blue Book price; then I'd use the engine work (which a knowledgeable buyer will appreciate) to close the deal (and further justifying the higher than Blue Book price).