Cofap shocks. Oil filled. LoPo. They work.
Take out moar air. Build up yer muscles.
Then (if necessary) take out small leaves. Bridget (my MGTD) has all six small leaves removed from each of the beam. Only the eight large leaves are left. Doing that took the ride height down (now a bit too much—six years later I'm probably gonna put a few back in!) but the ride quality—with lopo oil-filled shocks and 165/80-15 Nankangs running 16 lbs improved a bunch.
Speedsters have better weight distribution than Bridget. After the shocks (cheap ones!) and removing most of the air from the tires I'd start, in your case, by removing 3 small leaves from each beam. That will take the spring rate down to something close to ideal, but beware, as it will also give you more roll. You DO have the larger 5/8(?) sway bar up front, right?