The Seneca Falls integral countershaft and clutch unit was a well-engineered attempt to bring the benefits of a stand-alone machine to an existing design. Later machines, as below, used a similar system, but with a floor support and a jockey pulley to tension the motor-to-countershaft belt.

If you are going to run a flat belt from a motor pulley, it helps to have it wrapped around at least half the circumference …..
Older electric motors tend to be enormously large and heavy for their rating - heat build up was a real problem and, because the insulating materials of the time could not cope, some way of limiting the temperature rise and dissipating the waste energy was needed. The answer lay, partially, in making the motor large - so improving the ratio between volume and surface area.
The result for Seneca Falls was the need to built a massive platform on the back of the stand and support it with two substantial cast-iron floor brackets - and all for a 1.5 HP motor.