distributor curve springs?

For Street Duty
-I also, would recommend to swap the vacuum source for the V-can to Timed / Ported source, AND to make sure the V can is not working at all, at idle.
-Then I would start with two medium springs, in an effort to delay the "all-in" timing to 3500ish.What is important is to not bring in the advance too fast.If you have access to the dizzy-machine, just slam in whatever springs it takes to hit the target. If the engine accepts this with no detonation,then, at some later date,and, on the street, I might try to bring in the timing a little quicker. But if you do this;just don't bring in the N2O until further up the RPM band.N2O will kill the pistons real quick with too much timing.
-I would loosen up the V-can spring-preload, so that the V-Advance was all in asap.But I would experiment with the rate later, after the initial/power numbers,and the rate of of mechanical advance,are finalized;until then, I would leave it disconnected.
-The 16/30 setting is probably good for running N2O, but It is terrible for street. I would suggest a 18/34,or 20/36 street setting. Then,at the track; back the timing up and defeat the V-can.
-The 18/34 with a fast 20*can will pump up the low speed part throttle timings. This will,smoothen the torque delivery, and make the teener behave bigger than it really is, and return some good fuel mileage as well. It is the only way to get timing of 48* or more, at cruising speed, which is what the engine desperately wants.
Make sure your T-port is synced up, and depending on the cam, 800(like TB says),or less, is a good idle target.

The trick for a streeter is to give the engine as much timing as she wants, under all conditions, and not one single degree more. In fact two or three degrees short is better than 1 degree too much. This becomes a real test-of-patience, as it is or sometimes becomes, a moving target.
Some guys crank a ton of initial into it, cuz the engine accepts it. But the power-timing is more or less fixed in stone within a degree or two. Then it becomes a battle with dialing in the rate of advance. If you bring it in too slow, one might think you'd be missing some power. But if you bring it in too fast, and she gets into detonation, you get to start over. For this reason, I like to start with a slow curve, and perhaps with a little less initial, and sneak up on it over time.This way has three advantages.#1) the engine will live,and #2) you get to know your engine, and #3) you get to see how the mechanical curve interplays with the vacuum curve.
When you start to zero-in on the various numbers your butt-dyno, and ears may no longer be accurate indicators of what the engine is doing, especially if you have been doing some carb work at the same time. So......start sneaking upon her.