That's a big project , but reverse will be wonderful on the trike.
Rather than move the cams , water pump, thermostat and carbs/intake and 4* trigger wheel, It might be simpler to remove and swap the rear case and gears onto your Valk engine.
When installing the "new Goldwing "starter you have to be cautious not to break the reverse idler gear . DO NOT force the starter in place by pulling it in with the mount bolts.
Also when looking for the Wing starter remember to get one from an Aspencade or SE model. The Interstate version did not have reverse.
IIRC the Wing clutch slave cylinder is also different.
I didn't see if mentioned, a year on the Wing engine.
The Goldwing did not get the heavier built Valk transmission until I believe it was 1998.
I thought about the idea of making changes to the Valk motor, but when looking at the work involved what I'm proposing actually will be easier and quicker to accomplish. Plus, it would also involve splitting the cases to change out the shifting drum. I can get all the necessary parts for the reverse motor and have it all ready to go, then only need to swap out the motors. I believe the motor is from a '99 Wing and I know it was only the Aspencade & SE models that came with reverse(I had an Aspencade). Re. the heavier gears, they came with the '97 Valks and above, I don't know if the Wings got them the same year but would assume so.