With proper tapering and guy wires there's no need of fiberglass for a full size 80m vertical. Under the perspective of efficiency for such a lenght vertical, I wouldn't waste time with linear loading (or any other loading than capacitive). Go for top loading, fine tune and match the impedance with 50 ohm line easily at base, using a tapped coil between the element and ground. 73, Mauri I4JMY