It sound like the steering stem COULD be bent, but they are VERY hard to bend and it sounds like your forks had just a small bend... If they were all bent to hell, then I'd expect the stem to be bad as well.
In order to correctly check the stem, it has to be removed, placed on V-blocks and checked with a dial indicator.
When a 3 wheeler pulls real hard to one side or another, most times it is the rear tires. Different air pressure or use a fabric tape measure and measure the exact circumference of a tire. People don't realize that when mounting a tire they can stretch it very easily so who knows what the past owner did.
BEFORE doing anything, flip the left rear to the right, see what it does.
Of course there are wheel bearings, swingarm bearings etc etc, but it sounds like you have looked that stuff over.
Only other thing I've seen are frames themselves bend and only a new frame will fix that....
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country