ahh, I cant wait to build my own e-monster, and I always loved the looks of the cobra, though I was surprised to hear the drag coefficient was so high. Just a few things if I may...
Electric motors draw current directly proportional to load which is mostly determined by overall rolling resistance, but gear ratio also has a big effect so having multiple gears to choose from makes it much better for slow speed, stop and go type stuff even if you do lose a little power at the wheels due to drivetrain losses. However, for drag racing the direct drive is not only faster, it's also more durable, so it really depends on whether it's mainly gonna be a road car, or a strip car.
I've never seen anyone use an automatic in an EV conversion, probably for good reason, but you might be able to use a 2-speed powerglide and remove the torque converter, replacing it with a short driveshaft, basically the same way they sometimes delete the clutch in EV conversions. I'm sure it would require some fabrication and it might be more trouble than it's worth, but I know the basic principle is possible because I have seen it done on dirt track cars. I think it would be driveable on the road with no torque converter for the same reason you can drive an EV with no clutch, and even 2 gears is probably more than you need in that thing, but it would help with city mileage, since electric motors are happy running freely at a relatively high rpm to a gas motor.
While it is true that electric motors are more efficient at higher rpm, there is of course a sweet spot. The reasons for this are fairly simple, and it's been a while since I brushed up on it, but from what I remember the iron core of each pole on the rotor retains its magnetic alignment, and has some resistance to flipping its alignment each time the commutator advances. This creates heat in the iron core, but at low rpms its negligible. At higher rpms the iron core is having to realign its poles more often, and the extra heat generated in the core of the rotor is transferred to the copper windings which increases resistance. This is your enemy, both in terms of performance and efficiency. More resistance not only increases amp draw, but reduces power and torque at the same time. In extreme cases the increased amp draw creates so much heat that it creates a vicious cycle that can lead to thermal runaway which will melt your brushes and/or windings like a bus fuse, basically turning your motor into plasma. I'm not saying this is what's going to happen, but it would still be a good idea to get a motor temp gauge if you don't already have one just as a way to monitor efficiency. Long story short, monitor the motor temp in combination with amp draw to get an idea of how much load it's under, any excess heat is a sign that it's exceeded it's efficiency range or has just been run too hard for too long
also, drafting semis is a great way to reduce your wind resistance, combined with the front grill block, belly pan and windshield rake listed above should give significant improvement. I have the same problem in my vw rabbit (COD .44 i think, even though it's a brick on wheels it is somehow more streamlined than a cobra) and it won't affect the looks as long as you have good brakes
Do you have a video camera? Would love to see some footage of it in action if you can, keep up the good work!