Another timing curve question

I just read through the thread on Moparts which you posted in:
race distributor advance springs

It sounds like I don't just want to lock it out (since I do have an electronic ignition box), since I'd be leaving a lot of power on the table. One super-light spring and one heavy spring with a loop, then.

What do you think about this one for the super-light? McMaster-Carr
Wire .018", ? coils, Coil OD 0.240, Length 0.75", lb/in 0.78
Looks pretty close to the Mopar P2932675...

I have a heavy spring with a loop that I think came from the stock distributor:
Wire .046", 6 coils, Coil OD 0.279", Length 0.985" (measured inside the wire on each end). OK for the heavy one? (of course, I don't know how much retard will come from the Jacobs ignition box).

With those springs, do I need to keep the FBO limiter plate which limits on the outside vs. welding up the inside of the slots? Or just leave the unrestricted (stock Mopar) advance range (around 26-28 degrees I think) as long as the engine will start ok with 6-8 BTDC?

I'm surprised you have the secondary t-slots square unless it was converted to 4 corner idle, and even then might not want them square depending on how high up they are.

Could you explain in more detail? No 4-corner idle.