I'm looking for a second opinion on ignition timing specs for a GM 350 engine with a Mercury Thunderbolt IV(v-6) ignition and a roots type supercharger.

what did the first opinon have to say?

What boost, compression, heads, plugs, intercooled or not? Injected or carb?

Here is the set-up:
GM 350 ,162 b&m blower(6-7 pounds of boost),holly 4150 750cfm carb,lunati cam for super charger(custom built for marine use), mercury thunderbolt IV ignition(6-12 degrees timing),standard plugs for mercruiser 260

set your total timing at 34,blower motors like advance even at low rpm,i always use msd distributor and lock it out.

What is the compression ratio????

30-34* total depending on CR.

8:5-1

What would the initial or idle timing want to set at for the above engine set up

In my opinion 34 is too much with a non intercooled little blower putting out 7 pounds of boost with no knock protection. If it where mine and I was not going to set it up on a dyno it would not have but 30 degrees total as it just not worth the chances.
Allen

That would depend on how much advance his module gives. It looks like he is running a V6 module which will give about 10* of advance. Initial timing is really not that important.

I would set it at 30-32* total. Also I would change the spark plugs to 2 heat ranges cooler.