IIRC the 1850 metering blocks (the 600 vacuum secondary carb) will work. I would pin the emulsion and idle feed restriction and see where they are at. I’m certain the idle feeds will be smaller and that’s probably not a bad thing.
Below is from Andy from Unity Motorsports. He is running 660's on this truck. Great tuning info on those carbs. From Andy when I asked how he has power valves in his 660s.... "I ordered 4 primary blocks for a 1850 600vs Holley.. they work great but you must modify your baseplates to convert to have 4 corner idle mix screws.. if you don't want or need the 4 corner deal you can just bottom the mixture screws out and just use the Primary screws Hope this helps. Andy"