Lassa Fever is easily obtainable in the wild. It's found in humans and other mammals across sub-Saharan Africa. There would be no need for all this subterfuge.
Supposed expertly forged German passport blatantly misspells "BUNDERSEREPUBLIK" instead of "BUNDESREPUBLIK" (Federal Republic).
Although this episode takes place in early 1984, when Beeman and Adderholt are following William, they are driving a 1987-90 Chevy Caprice. Philip is driving a 1986-92 Volvo 240 (and passes another '86-92 Volvo 240 while he is driving, as well as a 1986-89 Honda Accord).