For my $0.02 I would say...yes to the shield, definitely yes to the horsepower and I doubt the top would be that useful.
Why, a shield is cheap insurance. Yes it probably will not be needed, but the results could be catastrophic if it was. Can you imagine a cop without a vest?
I have approx 450/450 at the rear wheels with a 393. There have been times when more would have been better. A 393, 408 or even a 427 will produce great torque and still be streetable. Big cubes = big torque and torque is what gets the train rolling through the gears. HP is mostly just icing on the cake.
I have put approx 1500 miles on my car and got caught in a sprinkle twice. It was really no big deal and I would not want all the snaps, hauling it around, the pains of putting up and taking down, the confinement when it was up not to mention the $1500.
Oh, the trans. Take the TKO and make sure you get a limited slip diff with a 3.4 to 3.6 ratio. A couple things that restrain torque are weight and gear ratios. I do not know the rule of thumb for speed gains related to weight vs torque but you gain a second in the 1/4-mile for every 930 lbs you loose.
The last thing you want is to have the smack put down on you by some frisky mom hauling the groceries home in a Hemi Magnum, 300, Charger, etc...
