The 10" will be fine for his combo. If he had a hot 340 in there he better step up to the bigger flywheel and bellhousing along with a good 10.5" clutch. Brewer has some nasty clutches for the 9.5" applications for horsepower up north of 500. Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists @Dan Brewer
