I'm not aware of any 4100's used for 1967, with the exception of the few 67' hipo's (489 units). 2100's were the main stay for the 2v cars and 4300's were used for the small block 4v cars, "A" codes in 67-68 . The same goes for Cougars and I think some of the part numbers cross over between the two lines. Big blocks received the Holley 4150 carbs that I believe were rated around 735cfm??
I have also heard of issues with the 4300's including "flat spots" in acceleration. But, some builders have supposedly worked these issues out. Pony carbs was one that claimed this but I do not know of anyone to back this up.. (and they have been out of business for sometime now). I have numerous Mustang specific 4300's as cores because face it, many folks want the original set-up now a days and they seem to be holding their value probably for this reason. I'm sure a lot of folks in the day replaced the 4300's with over the counter Holley's (600 cfm's)... Hope this helps