Complex sentence: The car went through a series of annual face lifts each given a Series number, replacing the Mark number used on the previous Minxes; there was no Series IV. The engine was new for the model with overhead valves--a first for a post war Hillman.
Split into simpler sentences: The car went through a succession of annual face lifts each given a Series number, replacing the Mark number used on the previous Minxes. Michael Sedgwich & Markes Gillies, A-Z of Cars 1945--1970, pages 88 & 89 There was no Series IV. The engine was new for the model with overhead valves--a first for a post war Hillman.