I was modifying my LGB Genesis to add MTH Dash 8 trucks underneath. Of course when I was finished and checked, the speed was way off (too fast). So I had to grind down the plastic housing to allow the tach gap to be closer. I bet the appropriate tach with med spacer might work? I just used the plain one that was already installed into the LGB.
So when I got done, it appeared to run the correct speed. I put it back on the track with my scratch 1 gauge F40PH that I also just upgraded to MTH trucks. I had run this consist last night before quitting. Spaced a few inches apart, the rear F40 engine accelerated and caught right up to the LGB? I had thought last night that the F40 might be slow so this surprised me. It occurred to me that I had run both the Genesis and the F40 out of the consist and may have changed the settings. So I reset the accel rate even though the consist still said it was set for #1 that I wanted, I pushed the scroll on the remote down again. This time they both ran perfectly spaced apart. So it occurred to me to share this here. I must have reset the F40 for the slower accel rate #1 as desired from the default #4.
When you try and speed match 2 MTH engines, make sure that the accel/decel rates are set the same. Otherwise you may wrongly conclude that they won't run together!