New Holley 4 bbl

Have been researching this topic of glowing exhaust on line and some say too rich, others too lean, also possible causes are; catalytic converter clogged, o2 sensor, throttle position sensor, cracked manifold or timing. The timing was off 3 deg but dont think that was problem...
Where to go next ???

X3 - forget the carb, you'll just spend a ton of money to get it right (maybe). Go for the aftermarket throttle body fuel injection system. They tune themselves and give much better performance, especially for an RV.

Holly now makes a bolt on throttle body fuel injection carburetor. That might be something worth looking into for you. I believe Edelbrock may also.

You might see if there is a third party replacement for the Holley that is more tunable (I'm thinking Edelbrock) but even that is going to require some expensive dyno time to get the jetting right for the pattern of use.

Living in California, dealing with CARB emissions standards and testing, can be a pain. In the carburetor era, it was hard to do a tune lean enough to pass emissions when the "solution" was lean burn technology, and still be rich enough under load to function well. U.S. carburetor designs simply did not have enough mixture control flexibility to meet the full. range of needs, particularly for trucks. That led the industry to electronic fuel injection and feedback loops in the control programs, abandoning lean burn for catalytic conversion, which for NOx control needed mixtures rich enough to provide useful power with a little bit fuel cooling.

Holley has a catalog of replacement carburetors. You can look up 1987 Ford Van with 460 V8 and there'll be an order number. Also, buried in notes and details, will be "not for RV use." I think they realize the load an RV represents and understand their generic carbs are not designed to accommodate it.

Double check the number is the correct oem replacement.

Wow, that certainly wasn't the new I was hoping for..
Welcome to Rv ownership...I guess ¿

Probably not.
It sounds like it needs re-jetting which is a daunting process for the person not accustomed to doing it and a time consuming one for those that are experienced.
If just adjusting the A/F screws wont fix the one you have, you might consider getting a rebuilt replacement carb for your exact application.