(p.s. if you think the 707 variants were convoluted, wait till you read up on 747s. Including the -SP there are 7 variants of the 747-100 alone: 747-100, 747-100SR, 747-100B, 747-100BSR, 747-100BSR SUD, 747-100SF or also known as the 747-100SCD, and the 747SP).
