From the beginning of production (when these engines were designed) in 1958 up until the 1973 model year the diameter of the thrust surface's outer edge (on the #3 bearing) will be approximately 3.470" for the "B" engine. Starting in the 1974 model year, this diameter was increased approximately .280 thousandths to 3.750" in order to give the thrust surface more surface area. To allow the new larger bearings to fit, the machined recess area in the block webbing and the main cap in which the thrust bearing shells fit was increased an equal amount. We refer to the pre '74 bearings as "Early" and the 1974 and later as "Late." It is possible to use the early (smaller) #3 bearing in all blocks, regardless of the year manufactured. Using the later style bearings in an early block is not possible since they will be too big to fit in the smaller machined recess area. All other bearings except the thrust (# 1, 2, 4 & 5) are the same for all years.