Re: correct msd springs
Just looked at the instructions that are available on line.
It comes with the limiter, so total advance (at the crank) built in is 21 degrees. So, while a dial back timing light is nice to have, in this case it isn't essential.
If you have a regular timing light, with the vac advance DISCONNECTED, your initial advance should be about 15 degrees. That will give you a total of 36. You can always check it later to see exactly at what RPM it is all in. Personally, I would set the initial at 15, use the weakest springs (Doug's advice for one heavy and one light may be exactly where you end up). Connect the vac advance to manifold vac and go drive it. If you haven't already read JohnZ's article entitled "timing 101" do so.
If it pings under load, go one step stronger on the springs. If it doesn't enjoy driving it.
One other thing, I doubt this will be an issue for you, but some engines don't like even 15 degrees at idle. If, when you go to start it hot or warm, it sounds like it is kicking back a little, you will need to use less initial timing, and use a different limiter (comes in your kit) so that you can use less initial, and still get 36 degrees total.
Also, some Chevy engines like 38 total, so don't be afraid to try a couple different settings.