I have not had a bunch of time to work on it, but I have got a little bit done. The wiring is not that hard, once I found good wiring diagrams for both it was fairly easy. I pulled the solenoid wire from the rear of the 1872 up to the front since the solenoid is on the CH18 starter vs in the rear by the battery on the 1872. I used the engine side harness from the M18 and the chassis harness from the 1863 to make a sort of patch harness to go from the new engine to the 1872 chassis.
For the "firewall" I am going to use the one from the 1863 and just trim it off where it meets up with the curved section of the 1872's firewall.
for the throttle cable I used the one from the 1863, it is on the opposite side of the dash between the two models, but the mounting holes lined up fine. I just had to mount the plastic handle upside down so it did not hit the steering column on the 1872. I moved the choke from the left side to the right so it would reach. I used an existing hole for a switch and just used washers to take up the gap in the bigger hole.
I will say it has been nice having the whole 1863 there to pull parts from.
Here are some pictures.
old engine getting ready to come out. I have re-attached that end cap on the muffler a couple of times, but the occasional backfire is hard on it!
M18 is out
CH18s from the 1863 is out
