New Short Block won't run

Any help appreciated. I have a briggs 28Q777-0678-E1. This is a 2000 15HP engine on a Dixon ZTR. The recommended short block is 697762. However, even though everything fit up great, reworked carb, lapped valves but the thing wont run. The SB fits model 28 and 31 Briggs engines, and the parts list show same flywheel, valves, head ect. for both series. :confused2:But it just sputters and back fires. Seems like it has the wrong flywheel, but that's not what the parts listings say?? I am stumped!