Pump alignment on direct drive is tight.
The problem is, as the engine makes "pulsating Hp",
and the pump is making "pulsating Pressure"..
between the two if a whole lot of stress on the shaft, and/or shaft key..
I personally would prefer to throw away a worn out shaft key every 12 months,
..to NOT have to "rebuild " the shaft "key-way" on the motor every year and a half.
We charge $50 to $75 to fix those shafts.
belt drive has a very efficient "pulsation-Dampening" effect,
So, belt drive is your best insurance to Long-Term-Low-Cost.. aka.. True Reliability
Class dismissed. :{)