@gunrunnerjohn posted:If the board can be reversible, why not?
The only wild card is where to position the optional resistor for LocoSound applications. The other consideration is the wiring would be backwards, so that would have to be made clear...
I think the pads for the resistor might need to go on both sides. Especially for the case of a spacer under the sensor, the resistor must go on the other side of the board. I don't have a LocoSound tach but it looks like an 0805 might fit (as shown below). It appears they violated some design rules placing the resistor pad overlapping the sensor pad depicted in red below.
I'd think a thin trace between the 2 pads might be simplest. Cut the trace (thin blue line) if installing the resistor. Of course you'd have to cut the trace on both sides of the board; or run vias thru the two SMT pads so the shorting trace is only on one side.
Since I'm not doing the work I can only make peanut-gallery comments, but it seems like the instructions to support either chip is much more complex than if just supporting the QRE. 
