However my seat does NOT have the extended pipe on the end. What is that for?
I've never been completely sure, but I've always thought it was to help smooth or buffer fuel pump pulses...maybe to help stabilize the needle a bit more (particularly on engines which don't flow as much fuel through as others). It appears on many Carter YF carburetors (if not most of them). Currently I'm going through a Carter YF 4145s and it also has that extended standpipe...about 2mm shorter than the one used in your carburetor. That carburetor also has some other interesting differences. More to follow. Unfortunately I have not been able to find much data on it...fuel inlet orifice size being one question. I may have to guess at that.
