From what I remember, the front gearbox is not restrained so it may rotate about the axle a few degrees, especially without a load being pulled. If you ever look at some brass engines, you will sometimes see a strap on the gearbox to the frame to keep the floating gearbox from hunting under no-load running. This also keeps the input shaft from over working the universals. If the engine isn’t jerking and otherwise runs smoothly, I would check it out under a light to moderate load and see if the gearbox settles down with a little torque. A video might be helpful. Keep in mind the front shaft is sleeved and telescopes so it allows a bit more torsional freedom in this setup. I sold this engine off a few years ago so you may want to verify the gearbox arrangement. You should see the top of it change angle with direction and load assuming there isn’t some other issue.
You can see the front floating gearbox in Allan’s photos above, angled forward above the center drivers.
