I'm running 205/55 tires on stock TR6 rims. I'm not sure the extra width helped all that much, but getting to a more modern tire size means you have choices in tread compound and construction that just aren't available in the old skinny tires. Bridgestone Potenzas were about the best handling tire I tried, but the Kumho Ecstas are a close second and give a better ride.
Offset is important when choosing wheels. I tried a set of aftermarket wheels the same width as the TR6 ones; but the offset was just enough different that they wouldn't fit with the 205 tires. The TR6 wheels are pretty close to ideal as far as stuffing as much tire as possible between the fender and frame. Even so, I did have to massage things just a bit, and the tires do rub lightly in hard turns. Not enough to damage them, but you can see the shiny stripe on the sidewall.
A front swaybar will help noticeably, too. Opinions are mixed on whether a light rear bar helps or not. On my previous 59, I felt that it did help on the street, but was a hindrance on the autocross course as it tended to unload the inner rear tire so I couldn't get power to the ground. A limited slip diff should help that, but the car got wrecked before I had a chance to try it.
The front bar made by ADDCO (and offered by various vendors) is about right IMO with no rear bar (and no other suspension mods). If you run a rear bar, though, you can go heavier up front too. I used nylon bushings to get more action from the ADDCO bar, but could have used more IMO. Richard Goode said he could bend me a custom bar in my choice of sizes, but I didn't get that far.
FWIW, I don't believe the spring rates were ever deliberately different side-to-side. Instead, the passenger side spring had a spacer incorporated, so the car rode level with only a driver. I don't know of anyone selling the "handed" springs; but you can add the spacer yourself if you want. It's just two sections of main leaf, long enough to match the pad on the axle and the same width as the rest of the spring.