In those funky 1950's, they took a turboprop Vickers Viscount and mounted two Rolls Royce Tay engines instead of the four piston engines. I assume this was a convenient way to test those jet engines. Was there any intention of actually producing this variant? How fast/cruising speed of this airliner mutation? Were any airlines interested in buying them? Could the propliner airframe and components take the higher altitudes, temperature and pressure differentials of pure jet flying? Drag and efficiency, fixed wings with jet engines practical or not? Was there any other commercial prop airliners that were mounted with pure jet engines?