Here's a description of yeovil according to Pigot's 1844 Directory of Somerset.
And here's a map from the 1st Ordnance Survey, from 1886-1901.
I don't have any of the earlier Yeovil handstamps, the first is straight-line handstamp from 1766, then two more straight line handstamps of slightly different sizes (BCC rarity Z), followed by an early single-line mileage mark and another straight line handstamp.
Then we get to the more common mileage marks, here's an example of the boxed mileage handstamp from 1803.
I must apologise for the terminology in the write-ups, they come from fairly early in my Postal History education - where the write-ups say "cancel" please read "handstamp" as the marks do not "cancel" anything. I now try to only use "cancel" when the postmark is cancelling a stamp or is a machine-cancel rather than a handstamp.