Second Hughes Converter desroyed??!

, are you using nitrous ??
Its a street car never used nitous

flexplate is this one:
TCI Auto 145200 TCI Forged Flexplates | Summit Racing
when I change back to the stock converter I have to use the stock flexplate aswell because of the 5/16 bolts, any issues using a stock flexplate behind a 408?

Sadly I am in europe and we dont have a local converter shop in every town and when i would find one it will be cheaper to buy a new converter by the time this guy opened it

The trans is fully built by a good guy with parts from A&A transmission, dont know whats in exactly. Im in contact with him aswell but he also is clueless why these converters fail, thats why I ask here.