There are two options for the engine location on the 1964-67 GM A-Body. The forward position works best with late model transmissions (i.e. T56, 4L60E-4L85E transmissions) since the engine is moved forward about 1". The rearward position works best for classic transmissions (i.e. TH400, and 200R4 transmissions) since the bell-housing is in the same spot as the Gen II Small Block engine.