The A or B in front of the displacement is a bore designation that GMC used and does not mean that the engine was rebuilt. GMC used the 361 from the late 40's until the mid 50's. However, it was offered in a size of trucks that never gained much popularity. Many people considered it cheaper to overload a two ton. Not many of the 361 engines were built. Few survived. The engines were too big to put into a pickup, so there was very little interest in saving them. About the only parts you will find will be NOS.
