I would bet money that the Ujoint cup flew out unbalancing the driveshaft which threw the driveshaft way out of balance and out of round,whipping the output shaft around which broke the tranny. I had the exact same thing happen during a burn out, one of the front U joint cups came out in high gear and split the trans case from the right rear corner across the top to the left front corner IHTH, as far as finding a push button these days, good luck If it doesn't have, which i'm sure it does, the slip joint trans yoke and standard Detroit type U joing make sure and convert it now Call a good custom trans shop like CRT, Turbo Action or your favorite Hi Po tranny bulider to get it built to hold your freinds paoer level safely, NO CHEAP PARTS BTW, 500 HP is not hard to make with mostly stock 440 parts, add a blower and look at 750 HP + very easily