67 notchback resurrection

well finally got the engine broken in/dynod she made 340hp and 360tq. looking at getting a higher stall speed for the trans but unfortunately have a 18 spline trans... Not sure if i should swap parts to 27 spline, buy a newer trans with 27 spline and have to go through it and than buy the higher stall torque, or look into possibly doing a overdrive trans swap.