About 6 months ago I aquired a 77 f-250 high-boy with a 351M, NP435 4-speed and 4:10's with limited slip. It's been well-cared for, and the 351M is remanufactured with about 60,000 miles on it. It has headers running to 2 1/4" straight pipes(no mufflers!), a Weiand intake(haven't looked to see exactly which one yet), Moroso carb spacer, mallory coil, stock distributor, I think it's bored .030 over, and I believe it has the stock cam. It has a 4160 holley on it right now, but it is time for a new carb as this one seems to be old and worn out. It's definitely the best running ford i've ever owned, good oil pressure and should have lots of life left. I don't know which carb would best fit my application, but I've narrowed it down to 4 carbs.
1. 1850S Holley 600 cfm vacuum secondary with non-adjustable floats. They call this one the 4160.
2. Holley street avenger 81570 570 cfm carb w/ adjustable vacuum secondaries and external float adjustment
3. Edelbrock 1805 650 cfm Thunder Series carb with adjustable secondary air valve( is this vacuum secondaries?)
4. Edelbrock 1405 600cfm non-emission carb with manual choke.
I would like the best power, drivability, and tunability from my 4-barrel. I'm guessing this motor makes around 250 horses (give or take), I drive it hard but the highest I've revved it is around 5,000 rpm's. I'm not sure what it redlines at but am not scared to wrap it out occassionally. With this set-up it seems like I could use some more low-end power. I'm not sure what I need for vacuum ports but it looks like PCV, Vacuum advance (distributor), anything else? Also, from my own experiences I want a manual choke, and from what I have gathered on this forum I want vacuum secondaries. Any info. is appreciated, I am kinda new to carbs but want to learn to make them work for me. Sorry for rambling, just wanted to get the facts straight.

 

Hello- Welcome to FTE! I have moved your post to the specialized forum we have here for your question. Check out the list of tech forums we have on FTE. There is a wealth of information and expertise here to help you. There are a number of links in my sig below to help you also. Have fun!

As far as size goes try the carb calculator here on FTE:
https://www.ford-trucks.com/calculators/index.php
500 CFM should be more than adequate for a 351M

 

The 1850 has external float adjustments.
I have had good luck with the Edelbrock carbs myself. I would try the AVS carb. It has mechanical secondaries, but had a spring loaded upper air flap that will not open until you are pulling enough air to need the secondaries. This eliminated the bog from them opening too quick. High performance Mopars used these alot in the muscle car era.

 

From the 4 carbs that you have listed there i would definatly go with the holley street avenger, i run a holley 670cfm truck avenger on my truck and i like it.