Convert Western Saddle to Regular Saddle?
Looks like there might be welding in your bike's future.  A competent welder might be able to attach some better seat stays that terminate below the clamp.  Then you'd use a normal saddle on a normal seat post.

BUT there will be a lot of unsupported seat tube poking up.  As a tall rider, I have over-extended seatposts leading to bent seatposts and cracked frames.



Your other option is to get your welder to make a bridge between the existing seatpost and the existing stays, and then mount a normal saddle on that using an old-school saddle clamp but rotated down.   

The risk here is the saddle will fall sideways if the bridge tube is round, so perhaps your metalworker can find some half-inch box section and mangle the bike clamp so it goes around a square profile.  

Edit:
Here's a spin bike with something vaguely similar.  The seatpost can adjust up/down, and the horizontal box section sits in a channel, and can't move sideways.  It can move fore-aft if the hold-down bolt is released.  On top of that is a short vertical round tube, where a normal seat clamp fits.