The factory switched back and forth offering four barrel then two barrel then four barrel manifolds year to year They couldn't make up their mind on what to run with each engine each year, sometimes they made a mid year change, although it is not always in the parts books. like in the california factories we would have a snow storm in the rockies and the parts train wouldn't get there on time so the LA and San Jose factories used to do a lot of mix and match. The real problem with the intake manifold is it weighs a ton .. It's almost a hernia trying to put in on by yourself. Cherry picker or almost chain hoist time. you have to check any used aluminum manifolds to make sure they won't leak coolant into the oil if you use the ford design carb they usually need to have the venturi and bore polished . a lot had die pattern shift and that can upset the designed air flow with the mismatch. once set up right I liked them better than the holly. Ford also put on a carter afb. they put out the most horsepower but the rebuild kit directions don't work,, You have to make sure the choke unloader works and that the linkage lets the back barrels fully open. and that the choke lock out of the back barrels functions and lets the back kick in when the choke is off. a mechanical link to override the vacuum when you push it to the floor is nice if you know when not to use it .