These threads always end up the same lol.
OP if you like NA power and want to stay NA for a while, go for it! The TB, with or without the Intake Manifold, will yield marginal gains (if any). It'll be more of a decoration than functional part. The intake manifold, as Jeremy stated, can yield some extra ponies up top. But I'm pretty sure if I remember correctly, the hotrods will flatline around 6300rpm, and fall on their face around 6500-6600rpm. So you'll have a 200-300rpm window where you'll have a flat powerband before you're just reving the engine for shits 'n giggles.
If I had to stamp numbers on the parts, I'd say 0-5whp for the TB, and 15-30whp for the mani (high end depends on fuel and how aggressively it's tuned, but I feel it's possible to squeeze 30whp out of just the manifold). Again, you're going to take a hit on the bottom end and low-mid range. It's gonna get soggy. Gearing will absorb some of it, but even with 4.10's if you stomp on it from 2k/rpm, it's not going to be less impressive than it is now. TB may actually hurt torque a bit depending on the tuner. If he just copies and pastes the throttle curve from stock, there's a lot more CFM flowing through a 62mm twin at 25% throttle than a twin 55mm at 25% throttle, if you know what I mean. More air volume reduces velocity at lower engine speeds, thereby reducing momentum of air resulting in less torque.
If bang for the buck isn't a thing, why even ask the forum. If it is a thing, don't do it. Let the next step for your S197 be out of the light, and into boost. Get a built shortblock and choose your FI for the block's best potential (usually somewhere around 600-800whp). No sense in buying baby blowers and wanting more down the road. Strap a D1 or F1 to the beast and you'll have room to grow into the blowers potential. Believe it or not, a F1 *can* make less than 10psi and be perfectly safe for a stock bottom end. Assuming the WG doesn't fail.. lol.