Those inserts are called "port stuffers" and were initially designed by Joe Lapine of Danbury Competition Engines.
I never saw them used on the intake manifolds before. Just the heads. I am very sure that they are intended to not only be epoxied in but "pinned" as well.
There was some testing done with them in the late '70s as I recall and some numbers showed around a 30hp increase on a dyno.
Their purpose is to reduce the volume of the intake ports on the iron 4v heads to about 230cc's.
Stock iron heads are around 250cc's. The primary purpose being to increase the mixture velocity to aid in lower rpm throttle response.
That helps with intake issues but doesn't help the exhausts.
Those are not 2v size intake ports on your closed down intake manifold and iron heads. 2v ports are smaller then that.
The A3 heads I have are similar as cast to the iron 4v heads with the port stuffers but are 220cc runners and have much better raised exhaust ports.
The intake manifold that was made for the A3 heads is an Edelbrock Torker type with matching reduced volume ports.
These are pictures of the comparison of the port differences on the two intake manifolds. You can compare those to what you have.
The A331 intake has no heat cross over provisions like the Edelbrock Torker does.
You can see that in the bottom view of the manifold.
The picture of the gasket overlay on top of the intake port is for the C302B aluminum head. That shows you how much smaller that port is in comparison.
Even though reduced in size from the original iron 4v intake port, they are all larger then the 2v ports. The biggest problem with the 2v port is that the floor is too low. It goes the wrong way. You want to raise the roof of the intake higher, not lower to get power from it.
