Pushrod selection

I am a 45 year old novice mechanic (Journeyman Electrician actually).I am learning automotive stuff now that lots of you guys learned in your teens so please go easy on me.
I have been struggling trying to get rid of valve train noise on my 360 since I changed the mufflers out this spring and found out how bad it really is. It is nice and quiet for about the first 5 minutes then it starts to tick like crazy. Actually it's quite a quiet tick but it drives me ******* crazy! The tick goes up and down with RPM.
I first looked for an exhaust leak. I crawled all under the car with a hose attached to my ear and my kids had big shop rags shoved into each tailpipe and I didnt hear a leak.
When I popped the valve covers off I felt the rocker arms had too much play both side to side and up and down so I replaced them all with a stock set of 360 pushrods I had from a junk engine even though they all appeared straight and pretty much the same length. This maybe helped a very little bit but likely did nothing if I am being honest with myself.
I replaced the lifters with new Melling hydraulic lifters (broken in properly) and the unknown spec cam looked good. The noise went away for a bit but on my first drive I cruised it for about a half hour nice and easy, then made a first gear pull to 6000 rpm like I always do at the track and the noise came back. I have been driving it around pretty gingerly for a week or so never leaving town or going over 2500 rpm and it is still the same. No worse, no better!
I need to pop the valve covers and check the rockers again. My question is, when ordering pushrod for use with the stock stamped rocker arms will each one be a slightly different length? I just picked up a pushrod length measurement tool (adjustable length pushrod) and will measure each one. Any help would be greatly appreciated!

Cley

The patient- 74 Duster street car. 75 model year 360 with stock rotating assembly, unknown cam, stock 1.88 valve heads. A-500 automatic with 4.10 gears in the 8-3/4 rear end. Cheap Patriot headers with good Remflex header and collector gaskets. 2.5" Summit exhaust kit with Flowmaster 40s (all welded now).