I just looked up some info on the Miata.
I hadn't thought about it, but the Miata is rear-wheel drive/longitudinal engine - the same as how many pickup trucks are.
I thought one thing that would be nice about a pickup conversion is how the motor would attach to the transmission would be a little simpler.
A Miata sure would weigh a lot less than a pickup and be cooler to boot.
A 72 volt battery pack by using Trojan T-145 flooded lead acid batteries would weigh 864 lbs.
Here is a Miata conversion using Optima 12 volts to sacrifice range for speed. I think I would want to flip that and get more range/less speed. Not that I want no speed, but it would be an acceptable trade-off for better range and low cost