I reused those items on the last to 5.0 builds. Check the push rods for straighteness and ensure passages are clean. Rockers are fine. I would suggest investing in new lifters. On my second build I had two collapse cuasing great glutious maximis pain.   For $120 investment, it's money well spent. Summit is your friend.

MS wrote:

Are they they stock pushrods from the GT40 engine?

No, they were from the stock 1988 5.0 engine.  Are the rockers, push rods, or lifters different on a GT40 engine?  I'm running everything stock below the cylinder heads.  

Roller rockers do reduce guide wear. They also increase valvetrain noise alot.  I have full rollers on my 427 but stockers on the 5.0 with GT40P heads  Nothing wrong with stockers unless you are in competition.

Rockers, lifters, and pushrods are the same HO to GT40. 

Cast valve covers reduce the noise from the roller rockers a lot.  With stock nonajustable valve train your options on roller rockers is somewhat limited.  I'd suggest the Crane Energizers.  These were OEM on the '93-'95 Cobra engines.  They are a 1.7 ratio, and should work without issues on the engine with GT40 heads.

Roller rockers reduce a ton of friction in the engine.  They free up some power as a result.  How much?  No idea, I've never seen a test where they didn't change the ratio of the rockers, so those results aren't going to tell us because they effectively changed the size of the cam.

I greatly prefer roller rockers.  By rollerizing the entire valve train you reduce as much friction in the engine as you can.  At that point you're basically left with the piston rings, which there's nothing you can do about.  IMO when they went to a roller cam and left the rockers alone they only did half the job they could have.