Having been in the automotive industry for many years,and having work many of those years on transmissions etc. It is common to replace tranmission,clutches,bell housings,rebuilt or repaired auto transmissions and we never had to worry about balance/spline alignments.However, every engine has at least 2 alignment dowls installed on the rear,so that when a bellhousing or automatic transmiion is installed it will be in correct alignment. Should one or both dowels not be installed then the bellhousing or auto trans will be installed shifted to much up or down or side to side. So that the trans input shaft won't go into the clutch,and a torque converter wont bolt up to flex plate or the converter hub wont go into the back of the crankshaft. The dowels were the only thing we had to make sure in place when puting things back together.
