I found the following device available in small quantities from digikey FDD3672 made by Fairchild. Vds 100v rdsON 28mOhm at 44 amps with Vgs 10v. I know the Vgs isn't great for you guys who want to run on 5 v but I am running on 12v so it is fine for the LT3750 which drives the gate to Vcc-2v during normal operation.

BTW I have my inverter built from your desigh BIGBOAT, it is running and I'm getting plenty of output voltage with it running at about 30KHz but the efficiency is not too great. It might be due to the core I am using which is an amidon FT-82-43. the -77 material would probably be better at 100 KHz or lower but all I had was the -43 material.

Let's see what the LT3750 can do. It is supposed to deliver 90% eff or so......