ZVS induction heater MOSFET failure?
I think I see your problem... You state that you had a 70 mH choke originally but then removed two turns to get down to the picture showing 40mH choke. I don't really think from your pictures and from your description of two turns changing the inductance that you have an inductance that large. If it's that enormous coil with electrical tape around it acting as your choke, then you have something in the uH area of inductance I would expect. How are you measuring your inductance? With an inductance multiple orders of magnitude too small and very likely a resistance equally small since there's hardly any turns on your choke, you end up with huge amounts of inrush current with no resistance or inductance to slow down your current. Right away you'll heat the mosfets up and blow them out.