I am going by memory but it will be close. It may be one of the 4300 series of carbs. The larger was 4300D and the slightly smaller was 4300C or visa versa. I think the throttle bores are the same, but the venturi's are slighter bigger for the larger cfm one. I have a 70 mach I that has a smaller version and I believe the 429 was a larger version. Smaller one was ~600 cfm, and larger was ~650-700 cfm. Also, beware!! Some of the 70 429 CJ motors came with a cast iron intake and a Quadrajet (as in Rochester). I had a 70 429 CJ with one. Almost swatted a smart A** parts counter man over that carb once. I told him that I wanted a rebuild kit for a Quadrajet on a 70 429 and he got really insulted (typical chevy man). He told me that Quadrajets were GM carbs and Autolite was for fords. I said O.K. give me a rebuild kit for a 70 cutlass with a Quadrajet----problem solved. In reality that Quadrajet had an "Autolite" tag on it.
I also think that some hollys came on them, but may have a "Autolite" tag as well. Google Autolite 4300 and see what you get----I will soon as I "submit" this post.
After a really quick search (http://mustangtek.com/4300/4300.html) , the closest thing to your number is C8SF-G or C8SF-H which are for 68 429's. Any C8** with an A designator seem to be for smaller engines. You may have been slightly off with the C857A number---check a little closer.
I was wrong in my previous post, the larger 4300 had a 1.25" bore while the smaller one had 1.00" bores.
I did a Google on Autolite 4300 and saw several sites, just go to all of them. LOL