you have to unzip the content of the pack into your Automobilista 2 main installation folder, it's the common procedure to install custom liveries nothing special.
great job. The Boutsen and Arnoux skins names do not appear correctly and are replaced with random names. To function properly you must remove the accents of the names of the pilots in the archives:formula_classic_g1m1.xml formula_classic_g1m2.xml and
F-Classic_Gen1.xml