Worst first drive ever.....

[72TealnWhite]

Bought a pretty nice 72' lwb 350 a few months back.. been working on it here and there.. mostly cosmetic .. Did do some minor tuning of the carb.. a edelbrock 1406 600cfm.. to get the idle right.. sounded like we had gotten it alright .. i had no plates yet .. so all i could gauge was a lap around the block. Had some small backfiring issues with it driving at minimal speeds.. and it would hesitate before acceleration... Well we got it to where we thought it should be and today was the day.. the test drive on the freeway.. It sounded ok. but it was hesitant still.. when it got going it sounded ok. It would backfire on decelleration or downshifting.. then i got going about 65 mph. got a thumbs up from a passer by and BANG !!!! sounded like i dropped a muffler... I looked and its definitely coming from the driver side.. i think i may have cracked the exhaust manifold... holy ****. what do i do now? The truck does run Flowmaster 40 series.. and it looks to have new pipes front to rear? Anyone know what could have caused all the hesitation and backfiring? and what about exhaust manifolds.. new ones? do i need special ones? pertaining to the block? Thanks in advance

nate