Hello, Roger,
It will be interesting to hear how you compare the Trusty to the Anzani once you’ve got used to it, but that’s something for next year!
Assuming the Douglas engine is the original it would be easier to date it from the tractor’s serial number. If you let me know I will add it to the Trusty Register and look it up next time I do the research.
My preference is for the JAP 6 as it has the same power and torque but weighs a lot less, but then you don’t have to listen to me!