Bottom line if it ticks at warm idle it is the worst tick, and this sounds like what you have. Read the threads in my sig, see poll results on 100's of rams, see if it helps. So what you could do is get a bottle of lubegard biotech and dump it in today or tomorrow, see if there is any change at all. Most ticks are at start up, and you say it doesnt tick at start up but actually after a while? Sounds like an issue and isnt the usual garden variety lifter tick. Ask your mechanic if he is sure he installed pushrods correctly. If you do have to crack it open and it is the pushrod, it will be very easy to identify because it will be bent if that is the issue.
It is the number one reason new cams tick and is very easy to screw up. We see this all the time, so it isnt a knock on the guy, it just is one of those things.