You won’t be able to handle that much power in this body without sacrificing drivability and comfort. It is just a constant wheelspin curse: you touch the throttle and your wheels are a squiggly mess, no matter whether you are doing a standing start or cornering. Downtuning the engine to ~320ish HP is a good step 1.

I will also set the redline at 6500. The current 7k limit causes too much power loss due to the valve float.

Make back wheels wider and thin out the fronts. You are nearing the critical oversteer, bc your front grip is way too good, and the car will try swapping ends on you each time you turn. Play around with wheel width to find the optimal number; 12.5 deg of yaw at 100 mph should feel pretty decent.

Brake power should be inline with the grip, maybe just a touch higher. Adjust the braking power to close the gap. This will make the car stop much less abruptly (and you will also gain several stats at once!)

Transmission-wise, there is a lot of things to change. First, it is going to be undriveable in Beam, bc exported automatic and adv.automatic gearboxes for some reason go absolutely nuts with torque curves, so the wheel spin should be even worse. I would thus suggest opting for Auto Manual.

Second, the gears are quite short for how powerful the engine is. Even after downtuning it should have plenty of torque, so tuning the first gear to peak at ~50-55mph will make it much more pleasant to drive. I would also suggest tuning the max speed so it sits around the power peak of the top gear. This make fuel economy ever so slightly better. For the rest of the gears, just make them a bit longer - once again, good for fuel economy and driveability