early vs late head inlet port size

[Waveblaster]

hello

I have two cylinder heads one 1964 early with the vents and I believe one late 1966 without. Skull caps are same diameter and depth essentially.

I was looking at the inlet port diameter and noted the early one is slightly larger (25.8 vs 24.8mm) at the opening and opens up considerably more internally towards the valve itself. Inserting my thumb the later is quite snug all the way through on the late. The early seems very open.
Looking at the inlet it does not appear to show signs of port work but I am no expert, you can still see the casting lines. Although someone appears to have tapped the spark plug holes to accept larger plugs, so it seems some work has been done.

Is this indeed a factory variation? I would have thought later models if anything would have larger ports unless the early suffered from some type of weakness in the casting due to thinner walls?????

Cheers

pictures below, Late model smaller ports first image. Difficult to see from images.

[G-Man]

Can you send pics of the combustion chamber?

305s have a squish area and 250s do not. Port sizes were different between the two.

G

[Waveblaster]

both have the squish bands. Assuming you are referring to the recess for piston. See below and also 250 head showing narrower dimension. The 250 head I have as smaller inlet ports again.

valves appear to be the same size?