...... I've tried spreading the lower yoke at the split .........I've been using a copper hammer, plastic hammer, wood blocks, etc. on the top bolt screwed into the tube........
All that sounds like the time honored methods. I'm assuming the wheel and fender are off.
How nice are the top fork bolts? Because in your more extreme case, it sounds like you need a 5LB steel sledge and a piece of smooth 1/4" aluminum to protect the surfaces of your top bolts. Why a steel BFH? Because the wood blocks or plastic hammer both soften the shock of the hammer blows. You need that shock to help loosen the taper.
so, I would do the wedge thing on your lower clamp. Then screw the top bolt in so there is only a small gap between the top clamp and the underside of the bolt head, and then hit it squarely with the hammer, protecting the bolt head with your piece of 1/4" aluminum. The weight does a lot of the work for you.
Sounds brutal, I know, but if you're lucky it just might come loose all by itself because it knows what's coming if it doesn't.