There are two sizes of hood - size 1 for smock sizes 1,2,4,5 & 7 and size 2 for 3,6,8 and 9. Size 1 are pretty common - size 2 much less so.
In terms of liners - old sizing runs from 1-5, new metric sizing is in the 180 (height) and 104 (chest) which is easier to work out. Old sizing 1 is c.170/96 metric to size 5 which is 190/120. Btw - these liners are not button in - I think on the experimental 68 pattern smocks this was trialed however production jackets ran with liners that are essentially separate.
Worked example: Size 9 smock needs size 2 hood and size 5 liner (190/120)
They look like this: