I recently rebuilt my twin 330 h.p 454's I went with .100 dome pistons to get the compression up a bit, stock cam, performer intake and stock carb and ignition. w.o.t is about 4500 r,p,m would the addition of roller rocker's make any noticeable difference? Thank's for any help.

These are 1990 non roller's also will they clear stock late model valve cover's

My 509 engines have Crane gold rockers and stock covers, with Merlin rectangle-port heads. I've seen several GM rectangle-port head/Crane gold/stock cover setups without any issues, but I've also had to use double-thick cover gaskets on a couple of engines I've done.
The addition of roller rockers will eliminate the weak link that's inherent with the stamped rocker/ball setup.

2 of the rockers will need to have the corners ground down for clearance for the V/C hold down bolt bosses. Even Merc does that from the factory.

If you mean noticeable difference in power, that would be NO. Might give you 5hp.

US1 Fountain is correct about the Roller rockers having to be trimed to clear the rocker cover. It is on the #1 & #8 intake valves. The left corner has to be radiused about 3/16" to clear.

at 4500 wot with fairly small cams the rockers would only be insurance against stock rocker failure (which probably won't be a issue). Grind off oil drippers inside valve covers and use double gskts,Smitty

Stock cam and springs won't overtax the stock rockers.
Rollers will give you a more rigid rocker (which you don't need with a stock cam), needle bearings and roller tips that can wear out over time and fail suddenly (whereas the stock rockers pretty much wear gradually not all at once), but they look cool.

High lift cams require either special stamped rockers or roller rockers. High spring pressures will kill stamped rockers.

Any ad that makes ridiculous hp claims for their rockers is just marketing jibberish.

Just changed to Jesel and the bolts were higher. Instead of grinding we simply ordered new V covers.

I agree with mcollinstn. You will not see any performance gain. You will most likely have to change rocker arm studs also to accomadate a roller rocker. And yes you will have clearance problems with roller rockers in a stock valve cover if you don't grind or shim up with gaskets. And if you are changing to rollers, I would want to go with a 3/8 pushrod instead of the 5/16 that you have in there now. I would also look at twisting that engine up some from 4500RPM. 4800-5000 RPM is fine for that engine. They are better than most people think.

Does triming the rockers change the weight distribution? If so, does the balance of a rocker play a role in the performance of the valves opening and closing? Just curious. I had Crane golds installed and chose to buy some new (used) covers that I did not really like because the ones I had did not clear. If I don't trim, what tall covers will fit?