At a swap meet today, person was giving away some old Harley accessory catalogs. I picked one up for my 04 RK. An 05 catalog, but close enough.

And in it, I found the answer to my mystery seat. I've a Reach Comfort Stitch seat. (insert silly happy dance here).

I couldn't figure out why the Comfort Stitch seat I had, had almost exactly the same dimensions as a Reach seat I'd picked up at a swap meet. Now I know. Back then, there was no uncomfortable "Reach" seat, it was done via the Comfort Stitch, and the Pillow Look. Both were available in the reach configuration.

PN 52973-04 for the reach Comfort Stitch, and
PN 52961-98A for the reach Pillow-Look.