The older ones have metal bodies. Also do an on-line search as there are many die cast plane specialists who like them. There is a man in Scotland named Les Veitch who has compiled a complete list of them. You are lucky because they are not expensive. The most expensive I have seen is a "Heinz Ketchup" Concorde.
There are some weird and rare castings such as a Russian Il-28 Beagle Bomber made for sale only in China by the firm SUTC (Shanghai United Toy Company) and the Concorde re-done as a Russian Tupolev 144 supersonic made in Bulgaria and sold in eastern Europe.