Torque Pro on Android with an OBD II Bluetooth takes a lot of beating. I know all the tech comes from the smartphone but you couldn't hope to provide HP, G force, GPS speed, altitude,acceleration, fuel consumption, water/oil temps and a host of other things without spending huge amounts of money.
You need to check Torque Pro with the OBD II adapter before you go further.
As you can't use a phone in the car then I suppose it is redundant (as a phone). If you transmit the data from the smartphone to a custom LCD display you would have something that makes a GTR dash look old world.
Just a thought, and people don't like techy boxes!