HEI TDC help working on truck

[NicoSlam]

I'm in the process of installing an HEI distributor on my 250. I haven't removed nor loosened the current original distributor so that I can identify TDC. the egine ran very well and started quickly. Well, the problem is that I'm able to position the rotor facing #1 cyclinder and the piston at TDC but the mark on the crank is 180 degrees off. If I install the new distributor how will I time it if the mark on the pulley doesn't hit where it supposed to. is it possible that someone install the pulley 180 off? Is there something I'm not seeing. Any help thanks