Starting 340 Build w/ Supercharger

For a streeter, I don't see a manual trans as an advantage. Typically you are limited at WOT to 1.5 gears. And the trip to 60 with 430 plus hp is really quick.
Take off will be the hard part; to co-ordinate the engines rpm with the clutch, to not overpower the tires. It will be all too easy to just light them up with a tiny bit too much throttle. IMO, getting the right TC will make for a more consistent,more enjoyable,launch.
I have never owned a blower, so cannot speak from experience. But I have seen some power curves. I would imagine that a 430 hp with a roots is more violent that 430 with a NA 360. The NA360 builds a long slow easy on the powertrain, curve.And its only 430 at the top of the curve and only for the space of maybe 300 or so on either side of the peak, before the curve decays,rapidly on the high side. And so finding an engagement point with the clutch, doesn't take a lot of work cuz the window is pretty wide.
Contrasting that with a curve from a blown engine, I see the power builds sooner and much more rapidly, and hangs on longer.And so your engagement window, when launching, might be a lil tricky. If you miss it and the engine is running away,well then your goose may be cooked, if the tires go up in smoke. If they don't,stuff usually breaks.
IMO, make it easy on yourself,go automatic.
And as to the 3.91s, those would be great for a NA application, where hi-way cruising is not required. But not so much for your application. I'd sell them if the blower is for sure.
Part of the appeal of the blower is the power curve.Lots of footpounds fairly early in the rpm band. This makes it unnecessary to have a lot of torque multiplication, cuz,well, you already have a lot of it. You'll probably end up thinking about ways to reduce the preponderance of torque,lol.

As an example, I run an A833 with a 3.09 low in it, and 3.55s. This makes a starter gear of 10.97. So, when I take off, if I dump it at 200 ftlbs, these are multiplied to 2194. This immediately breaks traction, and I control the wheelspin with the throttle after that. But if I slip it out at 150, being nice, then I'm just taking off briskly with 1645. If I blip the throttle and dump it, and let the flywheel do it's thing, then maybe she's at 1200ftlbs.So what I'm saying is that at lower rpms the power delivery is rather linear, predictable, and repeatable.My engagement window is from idle to maybe 3600 typically. The power with my 230* cam doesn't really wake up until over 4000. That is to say the climb is a little steeper after 4000.
Now try that with a roots. Firstly, with 8.5ish compression and a bit less stroke, the dump it and go thing is probably not gonna work for you.So you're gonna have to slip it out.But you're gonna need a few more Rs to get moving until the boost begins. But the boost will make the power curve climb faster than in NA mode. So you're gonna have to find a window that works for you. Probably somewhere between 2000 and 2800, guessing. And you'll want to be in that window somewhere, every time you take off. So in that case.....you might as well get an automatic with the appropriate stall TC (convertor). Then you can control the severity of the acceleration with the throttle,lol, and not have to concentrate on clutching.
Automatic kickdown is a blast too.
And for you, I suppose the overdrives are on the table too. Altho maybe not as useful a tool to you, as a smaller NA engine.
In your case, starting with a 318say and running an overdrive, would allow you the luxury of those 3.91s, and then a touch more boost. This would make your take off when normally aspirated (like 95% of the time) similar to the 340, maybe even better, yet the absolute power could be cranked to the same level. Then,on the hiway the .68 od would bring your Rs down to something like 65=2150, and now you're enjoying 318 mpgs, instead of crying the 340-sux-gas blues,lol. And the best part about this is 318s come standard with a blower-friendly compression ratio.
Anyway, like I said, I have no experience with blowers, so hang around and wait for the experienced guys to show up.