Ok I have a V6 auto gallant that won't start

Ok I have a v6 auto gallant that won't start. Owner was driving and t-belt broke at red light. Car ran ok before. The shop put a belt on and cap/rotor. Won't start-tell guy it valve related. Sells car to my buddy(mistake I tell em). In my shop now, lucky me.
So I have spark, spark tester, plugs were fuel soaked, replaced, each cylinder has 145++ lbs compression. The timing marks line good at tdc. Rotor button points to one on the cap. Took off valve covers check each cam and watched each rocker arm open/close the valves. All seamed smooth. Reassembled all and cleaned intake. Still no start. The only clue I have is that during cranking it sounds smooth/normal till I stop, then it does a short backspin. One time it even backfired thru throttle body. Usually I'd suspect timing issue but. Stumped and running out of patients. Can someone help? Thanks. Paul