Yes I did.

It is a new Holley 9022 double pumper marine carb. I believe 850 CFM, maybe 800. I have timed it three times. At first it was set at 10 degrees BTDC and now it is at 8 degrees BTDC and there were no changes in top RPM speed. I haven't checked to see if it will rev to 5000 in neutral. Is that safe or do I risk blowing it up not having a load on it? I have been told that IF it has a rev limiter it would kick in at 5000+ RPM. It is a T-Bolt V ignition. I believe it was in base timing mode. The strange thing about that was the purple/white wire had a bullet terminal with a rubber plug in it located at the top rear of the block but there is also a purple/white wire running length wise from the rear to front on the side of the block below the spark plugs in the same harness going to the alternator. It terminates mid engine and has a rubber 90 degree boot on it as if it is supposed to be hooked on to small screw threads or something. Regardless I grounded out one and then the other but I did not notice the timing change when I did this. It stayed at 8 degress BTDC at idle. We did confirm that the timing advances to a total of 33 degrees BTDC.

I've been thinking about this for awhile and looking for some opinions. As you know I replaced my 7.4L 310 HP engine with a 502 Indmar 420 HP. Once installed I fully expected to have to go from my 21P prop to something along the lines of maybe a 23-24P. But what I found was I am only able to get 4300-4500 RPM's out of it. My previous engine used to turn at around 4200-4400. Should I really expect to drop down in pitch to get a couple hundred more rev's out of it and improve performance that way?? I would have thought the 502 would have been able to over rev with the old prop. ?? Any thoughts??. I've been going down the list of "low RPM at WOT" check list and so far can find nothing wrong.

It will be safe to throttle it upto 5000 unless there is already a problem with it. I wouldn't hold it there very long, but you should be able to find out where the rev limiter is if it has one, and if it will go past 4500. There are so many reasons that can cause it to not rev past 4500, like timing, distributor, valve springs weak (were they replaced), carb, timing chain off, vacuum leak, low compression on a cylinder, to name a few. You should be able to run a 23-24 pitch prop up to 5000rpm with that setup. If you have a prop to try I would put it on, but you will still be stopped at 4500 the way it's running.
Do you have any or all of the details on the rebuild? If so post them. New valves or springs, valve job, pistons or rings & bearings, new timing chain, etc. Check the rev limiting in neutral, and after that I would start with a simple compression test. A vacuum leak at the intake will cause a major loss of power. Were the heads decked, or the intake. Was the intake new or purchased used. So many possibilities.

I will check to see if I can rev it to 5000 RPM. My gut feel is it will with no load. I'm thinking something is causing it to lose power rather than something limiting revs. FYI the engine was a complete rebuild. Long story but it was a new engine with less than 8 hours before it went in for the rebuild. I purchased a fuel pressure guage and vacuum guage that I plan to test the fuel system with. I think I will also use carb cleaner?? to spray the intake manifold and confirm that there are no leaks.

That sounds like a good place to start. I'm curious what the vacuum at idle on the intake is also. If it is low, then it indicates many potential problems to troubleshoot.

TA is definitely a premier Buick horsepower shop.
The guy in California, though, is well known in vintage Buick circles. I don't like to name names when something didn't turn out as hoped.
I wasn't involved in the selection of the builder, I was brought in when the car builder couldn't get the customer's motor to run worth a darn.
The things I saw in that motor make me want to NOT RECOMMEND that shop to anybody, but since I was not part of the conversation and was not involved in discussing the scope of work to be done, I cannot place blame directly. All I know is that even "good" shops can put an inexperienced employee on your motor.

It also is an indication of a high performance engine is it not?

Yes it is, but a stock 502 doesn't have a real big cam and should have good vacuum and not be jumping around.

Not to butt in... I have recently ran into a performance issue with a rebuilt 502. Just a thought but it in my case the valve stem in the heads are now a little long after freshening. When the valves were lapped and valve seats trued up the valve sits a little further into the head marketing the valve stem a little longer on the spring. This will not allow the valve to shut completely which bleeds off cylinder pressure. It may run but not have the full power. The correct way to fix is to shorten the valve stem. Other options are shorter push rods or shims under the roller rocker. Like I said just a thought....