Slant six timing.

My distributor failed and now I gotta redo the timing because I'm way off. I noticed I don't have a timing mark anywhere.... I've tried finding tdc on the first cylinder and I failed miserably. Is there something that i'm doing wrong?? I took out the spark plug and I thought I had it on tdc but I was wrong.. I'm lost and don't know what I did wrong. It's a 225 73' dodge dart custom.