Make it a trifecta, LCA stiffening plates, 11/16" TR, 4 link triangulated rear suspension and US frame connectors, wait that's four stellar solutions, Oh well. Not.

You have your mind made up, go for it, the vendors need the cash flow.

I drove a 2015 Challenger R/T Scat Pack, I believe it has a 12.3:1 ratio, and even that was very nice. I wonder if 10:1 may be too fast...? Does it make the car harder to turn if it has a higher ratio (may be a stupid question but I'm new to suspension and steering)?

As for the gears, what ratio would be better for a GV?

I haven't decided on the tires, I don't even have the car yet. I'm in the process of building up the cash to buy the car, and I'm planning out the build in advance so that I know exactly what to do and what to buy once I have it. What size tires would be ideal for a good mix of speed and handling, and to accomodate 17" or 18" wheels?

Probably 18" rims since high level performance DOT wide 17" tires are disappearing.

Think 275 wide in the front as a starting point. In the rear, I don't know what people can fit in there with a low stance. I'm sure 275's will fit. I'm thinking 295's with fender lip and offset hangers?? And I you mini tube and relocate springs you can get much wider.

Steering ratio does not make the car go faster or slower. It's the driver's preference and whether he can make the car go faster or slower with certain ratios.

I'm sorry, I don't know what you mean by trifecta, LCA stiffening plates or 11/16" TR, would you please elaborate?

The new challengers have electric power steering with a couple different modes to change the driving feel. Be hard to simulate that with a normal steering box, i would think.

too bad you are so far away Dan, I'd love to get whooped by your challenger!

Good info, thanks. And I know it won't make it go faster or slower, I just want to know if it'd be harder to steer with a 10:1 ratio vs a 12.7:1

Harder to steer, if you are using power assist, no. However, what fast ratio steering does is make a car feel "twitchy" and very sensitive to inputs at higher speeds. At 75 mph highway speeds, it may feel like you can change lanes by flicking your wrist. Generally speaking, the higher the speeds the car is used at, the slower the steering speeds tend to be. Uber fast steering ratios are great for autocross, disasterous for top speed events.

I'll share a few comments based on running a similar car (Challenger, 496 EFI, 5 speed/20% OD, 3.23 rear) on the road and HSAX course a little bit.

In terms of stiffening, the frame connectors are a start. There is benefit in reinforcing and stiffening the K frame also. Firm feel did mine with gussets, plates in failure prone strut and LCA mounts and full welding. Torque boxes help and also believe plating the LCA's helps.

The 3 speed auto + GV + 3.23 should put the gear ratios about where you want them as long as your cam is not too wild (what cam?). The ~20% overdrive will be a "top speed" gear or close. For cruising you could handle more OD with the stroker or lower numerical axle ratio. For sustained hard running (road race, Silver State classic ect.) you will need a low slip converter and good cooler to keep transmission temps reasonable and keep the transmission alive.

It will be a seriously fast car. I would not personally want super fast steering in that application. The stock ratio with a smaller steering wheel would be my choice. Also the fast ratio arms limit header choice.

Brakes sound good. I run a Cobra based kit with 13" in front and 11.7" in the rear. I started with Bear front only and drums in the back. Not the best. Hard to balance and I burnt up the drums at a track day. I installed the Dr Diff rear disc kit and a huge improvement. With the brakes you choose, need to check piston area, especially on the front. The Cobra based kit has smaller piston area vs stock Mopar and needs more hydraulic pressure. I wound up changing to a 15/16" master + dual 8" booster to get my setup to 100%. Hydroboost is another option.

Good luck!

...snip...

I solved the fast ratio arm and header problem, I found headers that will clear them.

Thanks for the advice!

Which headers are those? Are they big enough to not hinder a 512 cubic inch motor?

Probably 18" rims since high level performance DOT wide 17" tires are disappearing.

Think 275 wide in the front as a starting point. In the rear, I don't know what people can fit in there with a low stance. I'm sure 275's will fit. I'm thinking 295's with fender lip and offset hangers?? And I you mini tube and relocate springs you can get much wider.

Steering ratio does not make the car go faster or slower. It's the driver's preference and whether he can make the car go faster or slower with certain ratios.