If the 2-155 has the dual speed PTO, the answer is yes. They all used the same tach, but the 2-155 came the single speed 1000 rpm pto as standard equipment, and the later 2-135 had the dual speed. They look pretty much the same from the outside. The easiest way to figure it out is to remove the pto shield and see if the 1000 shaft has a sealed ball bearing, or if there's just a seal. If you can't find the outer edge of the bearing, then it is the single speed unit. Chances are it's a single speed 1000 rpm unit, unless someone has switched it over like we did with our 2-155.

The PTO readout on the digital tach uses the same pickup off the engine, it just recalculates the signal for the PTO speed, based off the engine speed. You could put an adapter on the 1000 rpm shaft, but I think the engine only turns like 1200 rpm to get the 1000 rpm pto to turn an actual 540 rpm.

Hope this helps.