72 350 wont start

    i replaced cam and lifters on my 72 chevy truck and cant get it to start now theres spark to the plugs but it doesnt start, also im getting blowback through the carburator could it be my timing or maybe i alligned the marks on the gears wrong. im pretty sure the marks were facing each other though. i even double checked no 1 piston on the fire position and adjusted distr.            any suggestions?

if you getting backfire from the carb...it most likely the timing. did you put your spark plug wires back in the right order??