Started my 340, IT KNOCKS! fresh rebuild HELP!!

4 speed tranny ... No its not the tap tap tap of a manifold leak. I did retard the timing seemed to help... But she still Hammers in there. Sounds like lifters with a screw driver in my ear on the valve covers, but why would they be clunking now?? same ones no changes.. Non adjustable.. stock?
oh man and I was hoping to puller out today..........