Big problem :(

[78' Silverado]

Well we started puttig the cam in today. Came into a big problem. first off were runing a Summit 383 Crank, 6 in. Scat Rods, and a Comp cam .630 lft cam. Well the first 3 lobes on hte cam are hitting the the #1 and #2 connectings rods. Is that b/c of the crank having to much stroke? Wat would the problem be? The cam spins freely but when spined w/ the crank it hits. Now thats at top dead center on number. Will adv. and/or ret. the timing get rid of this clearence problem. Or would it have to the with the cam to crank center line? Right now we 4 1/2 in. Center line from cam to crank. I have no clue wat so ever on wat the problem is. I figured, it would slid in no problem wat so ever. But, wat yalls advice on this problem? Is the cam to big, is my Crank, rod to cam combo wrong. The block is outa of an 86 Burb, and its a 1 piece rear main. Help me guys!! Thx

Tyler