Greg has me pegged.
The variable speed motor would be to more accurately match the combustion air to burning coal rates. The standard fixed speed standard factory selected speed will work just fine. My comment about tappings is indeed for an additional boiler water temperature well. I've got a indoor-outdoor reset aquastat (Honeywell AQ475A) that adjusts the boiler water temperature as a function of outdoor temperature. The boiler water sensor can strapped to the supply pipe or in a well. The well is better, but you need a spare tapping. It should be on the top of the boiler.
The Eshland (predecessor company to AHS) spec sheet for the boilers had choices for tappings. I assume for piping location options and steam operation which requires additional accessories like low water cut off. My boiler isn't like many cast iron boilers that have all the tapping drilled, tapped and then plugged. They are just not there. Again the standard factory choices will work just fine.
The belt drive option is a good one because it eliminates the conducted heat path to the motor bearings. Others have the cost for the option is not worth the cost. They reason it's cheap to change a heat damaged motor bearing. My boiler has the belt option.
My boiler has the standard grate timer. It works fine. The thermo ash monitoring was not available at the time. It's an improvement, but an expensive one. For those on a budget buy the timer and upgrade to thermocouple controller later. The factory uses Fuji brand, other brands are much less expensive. Retrofitting requires some mechanical and wiring skills.