The carb you bought (YF 2100s) SHOULD have the larger, 2-15/16 base. That one got swapped at some point in its life to the smaller size.
All is not lost. It shouldn’t be impossible to find a donor or stand alone throttle body in the correct size/casting number. Let me look through my photos and see if I can find the number you’d be looking for.
Nathan, From the pics Matt posted, it shows he purchased a YF2100 - not the YF2100S. IIRC, the YF2100 was sized for the 216 and YF2100S is sized for the 235. You are correct that the YF2100S shoud have the "1-788" casting number on the throttle body. Jon "carbking" and others will probably chime in here to clarify the info.
Matt, Jerry "Hotrod Lincoln" is right on the money that the smaller 216 rated carb isn't what you need for the 235, even if you change the throttle body to the larger size. You need to locate a "YF2100S" like
this one. That linked "carb" is just a sample I found on line in a short search. There are others out there if you search more.
