a 350/351 should get a 650 Holley. Race cars get large carburators but Nascars have restrictor plates to bring the air flow back down.
I would get a Holley 4150 650 carburator. You have the choice of vacuum secondaries or mechanical secondaries. I would take it to a guy who has a mastery in carburation.
My next choice would be a Holley Street Avenger 670. It is in my opinion a regurgitated 4150 650. I am angry with Truck Avenger for not taking more forms. 470, 670 and 770 really doesn't cut it with me. 470 cfm is great for a smaller engine of 235 to 260 cubic inches. That means this 470 Truck Avenger goes on a 250 I6. Ford a 289/302 I would get the Holley Street Avenger 570.
I have seen plenty of Broncos going up and down hills and crawling over rocks that had progressive Holley 4-barrels that weren't Truck Avengers. Now I think the Truck Avenger is a great carburator.
I am just saying that:
-the carburator must be sized correctly
-the carburator must be set up for the application by someone who is good at carburation.
-the carburation expert will know what works and doesn't work offroad and under various operating conditions.