lifter noise????

I built a 360, retrofitted the magnum heads on an LA block following the articles from Mopar Muscle and Ma Mopar. Using all the parts from Mopar including lifters and pushrods. Now I have the engine running and there is a 'tick' noise that circulates through the valve covers, and about 80% of the time.
I have checked the exhause and there are no leaks, lifters don't seem to be bleeding down either. I've been told to replace lifters anyway, check pushrod length, try 30 wt oil.
Has anyone else had this problem?
Thanks,
Eric