The 9" brushed DC motor is certainly not too powerful - when used in a forklift, it's no fire-breathing monster, and is weaker than the van's stock engine. It can be powerful enough if run much harder than it is in a forklift, but it doesn't have to be. The size of the motor is a bigger issue; yes, they're stupidly large.
Kei vehicles have little engines. That looks like a pre-1996 Acty, so likely 28 kW at 5,300 rpm and 54 N⋅m of torque at 4,500 rpm from a carbureted 656 cc engine. They were never intended for highway use, but that was enough power for the way they were actually driven, so if that is enough for you then the same from an electric motor should be enough, too.
The AC-35 at 96 V can only produce more power than the stock engine briefly, due to overheating, so it's unlikely to be an acceptable replacement for highway use, but for short periods it is substantially more powerful than the gas engine.
Kei vehicles have little engines. That looks like a pre-1996 Acty, so likely 28 kW at 5,300 rpm and 54 N⋅m of torque at 4,500 rpm from a carbureted 656 cc engine. They were never intended for highway use, but that was enough power for the way they were actually driven, so if that is enough for you then the same from an electric motor should be enough, too.
The AC-35 at 96 V can only produce more power than the stock engine briefly, due to overheating, so it's unlikely to be an acceptable replacement for highway use, but for short periods it is substantially more powerful than the gas engine.