I too built a pair of KEFs [concertos] about thirty years ago and I
still use them. The kits contained the front panel with drive units
and crossover ready mounted and wired and you built the box to a
specification. There was a range of sizes you could build with the
larger one giving a slightly better bass reponse. In those days you
could avoid purchase tax by building the cabinet yourself. They cost
£30 I remember :-)

Robert