Spring rates for 69 rear end

I have a 69 350/350 convt. that is practically a LT-1 (headers, highrise, holley, etc.) in every way. In fact I'm biting the bullet and running 25% 110 octane to keep the 11:1 compression. I'm about to replace the rear leaf spring (since I drag the exhaust when I open it up) and I'm debating if I should go with the 330, 340, 350, or 360lb fiberglass replacement. I hate to sacrifice ride quality too much since my wife really enjoys the car. Any thoughts on my choices? Also, bearing in mind that it is the original 70,000 mile spring, what kind of change should I expect?

I'm going to replace mine this summer. I have a 69 350/350. My rear spring has no arch. I am headed for the TRW 340 fiberglass rear and the grand touring springs up front. If you go with the fiberglass, wrap your pipes under the spring with heat tape. You can damage the spring with to much heat. Want to do all the rubber replacements with urathane as well. Let me know what you end up with.

I'm leaning toward the 340lb as well. I'm hoping someone out there can tell me how it rides. Thanks for the tip on wrapping the exhaust, I hadn't thought of that.

Why not shhot an email to places like Vettes brakes and ask them? Since they sell them, they should know