Complex sentence: The first prototype was rebuilt to production standard and "1458" was used to test a new nacelle design, which was un-armoured, had an enlarged fuel tank and a shorter fairing obviating the need for the tip to fold.
Split into simpler sentences: The first prototype was rebuilt to production standard and "1458" used to test a new nacelle design. This was unarmoured, had an enlarged fuel tank and the fairing was shortened, eliminating the need for the tip to fold.