There appears to be some extra linkage behind the main throttle arm on the 112-117. I assume that's probably choke or idle-stop related to the original Chevrolet application for the 3310.
Pro tip: The throttle bore sizes are the same from 650-800CFM. The super-common 1850 (600CFM) is too small. For those reading along in silence (lurkers), no you cannot use a mechanical-secondary baseplate.
I tried looking on eBay and was surprised that there were not two thousand aftermarket options (Proform, QFT, etc.) available for considerably less than the Holley part. When I needed a new base last year, I found them so inexpensively I bought two--one for the 9381 on the car, and another to reassemble the 4780 from which I'd robbed one. They were about half the cost of the 4160 units I'm finding and had Holley casting numbers (genuine?). I believe they were AED but can't swear to it. Somewhere on this board is a review of them; the quality was good.
Proform #67269 was the best deal I could find, albeit I did not get nearly as in-depth as I did when I needed one. The one linked was the lowest price; you may be able to find a better-priced AED or QuickFuel option with more digging.
Now for the opinion for which you didn't ax: Were it my carb, I'd spend the extra for the new baseplate. Right off the bat, everything is
new. No shaft-bore or linkage/pivot wear, etc. Changing/servicing the throttle shaft isn't a lot of fun. The old throttle-plate screws must be ground to be removed and i assume you've no way to stake the new screws as original. That means threadlocker and prayer. Also the spring can be frustrating since it's preloaded--it doesn't just slip on there. The throttle plates do not automagically align to the bores; it takes some futzing. I like to be cheap wherever possible, but this is one of those "
how long do you want to f__k around, and how mad do you want to get to save $70 and still have any other existing issues?" situations. It's your time and your wallet; your results may vary.