Looking for extremely high power dc motor controller solution, 120 VAC to 90-180 VDC, 5-10hp range
Doing a conversion from 12 V to 120 Vac and then back to DC is not the way to go. 

You mention that you will be putting multiple 12 V batteries in parallel to get your total power storage (AH capacity) and current capability ...why not put them in series and get the DC voltage you have up to a more sane level.
I'd aim for at least 48 V DC from you battery system.   

Using your figures:
40 A @ 90 VDC is 3.6 kW
At 48 VDC you will consume about 75 A at maximum power. Not insignificant, but perhaps more manageable than the 300 A you'd need at 12 V.
From there you could use a large DC-DC convertor to boost the voltage to 80 - 100 V without having to deal with insanely high battery currents. 

There are lots of 48 VDC electric bike motor controllers, those with BLDC motors would seem a much better bet.