hamonic balancer hitting

need alittle help, i got a 360la engine about 8 years ago and it was sitting in my garage up north, i moved to florida and my son had bought a duster to put the engine in. we took apart the heads and front of engine like timing chain and gears and pulleys, well he got a good deal on a 318 and so the 360 engine just sat until now where we just rebuilt it to put it in the duster but when we installed the harmonic balancer that came off the engine, it now hits up against the timing cover where the marks are, is there a spacer we forgot to put between the balancer and bottom timing gear? don't understand why it is hitting the cover now. thank you