Complex sentence: It was only called the Mark I after the Mark II was released, abd the original 3000 was built from 1959-1961 and has model designation BT7 (4 seat version) and BN7 (2 seater).
Split into simpler sentences: It was only called the Mark I after the Mark II was released. The original 3000 was built from 1959-1961 and has model designation BT7 (4 seat version) and BN7 (2 seater).