472 blows out 12 bolt!!!! help

[66trkbldr]

last week end swapped out 456 posi geared rear end for a 308 open geared one. Reason being that the 472 power plant screamed at 3500 doing 45 mph. 308s dropped to 3200 @ 55. truck was set up to run @ track but now enjoy cruzing .472 now puts out 408hp and 601 ftlbs of tourqe @ fly wheel ...th425 trans has got reverse man kit ect ect ...... fun but not for diff thus blowing the cracked spiders out the cover. pinion shaft still looks good no scratches trashed every thing else . Question ........ do they make smaller gears to help my highway driving other than a 308 and is there any differance in pinon shaft sizes between the carriers. can i run gears and carrier from 12 bolt car in 12 bolt truck housing. didnt evan get a chance to lite 1 tire yet. did put on bout 300 miles since installed. (4 shows in 1 weekend).