Around Nashville, stock appearing is usually stock carburetor and must look stock from 5ft away. You'll find a lot of places running classes called Predator Mod or Super Stock which are mild stock appearing classes that may have a claim rule on the engines.
Most of the opens are restricted to 4-cycle industrial-based engines, no 2-cycle, mx, snowmobile, motorcycle, etc. Some may allow billet blocks but it's really overkill for local racing and the track are usually bullrings, so you'll never get the power down.
Outside Nashville, it's a mixed bag of rules. Stock Appearings will sometimes allow GX390 carburetors and some of the MARS series will allow any carburetor that came stock on the engine, so if you have an Animal or a Shredder Engine they had factory slide carburetors. Georgia Stock Appearing has a ruleset posted on their Facebook page, their rules try to reduce more costly modifications, mostly to the head.
Opens for big race events and money races are usually restricted to 14.5ci unless you run UAS. Other rules may restrict modifications to cast blocks and cast heads.
We're in Dickson, Tn not far from Nashville, right off the 163 on I-40 if you need any help. www.eccarburetors.com
not much different where we are in Louisiana, I run my S/A in small block open, I just put a flatslide carb on it. Some paces we run in Mississippi and around home wont let you run billet heads but in Batesville at the nationals there were a lot of billet heads there, and I saw where it didn't make any advantage because we outran all of them !!
In western KY stock appearing rules were 1. must pull start 2. must run gasoline 3. 365 pounds 4. No external billet parts 5. must use a small block carb and 6. yes it must look like a small block engine from 5 feet away. I did hear the other day its being opened up to alky and electric start but I don't know if its true or not. SBO has a 14.5 cubic inch rule and thats about it.