Hi Jo, that engine has come out very nicely. A great job of a beautiful finish.
Those air chambers are for pulsation dampening and also to reduce cavitation damage due to the low pressure at the inlet due to acceleration losses. With such small pipes, there is not much mass, and with slow speed engines, the pulsation forces are generally low enough to ignore. They are easily added later when you have the material without any issues.
A larger engine, with a long inlet or discharge pipe can be a different matter, and those pulsation are quite capable of damaging piping and even engines.
I am still admiring those pictures and learning some of the features you have included to achieve such great appearance.
MJM460