New AODs have not existed since the mid 90s.
I can't really say there is a best place for a rebuilt one either. Can't even say a rebuilt one would be a good choice either.
I have to ask what makes you want an AOD. It is generally a miserable transmission. There are better choices out there that work better and can be done for less money. The 4R70W has been a go to choice for 20+ years now. Lately the 6R80 has been getting a lot more popular as well.
Do you have (or will have) proper axle gearing to work with the overdrive? What size tires are you running (or plan to run)? Same question for axle ratio? If those are not matched right the transmission will not work right. It will drive like crap. Stock axles will almost always be a poor choice for axle ratio, and still doesn't tell us much as there were multiple different ratios available when new.
306, so a rebuilt 302 that has been bored over. What else do you know about the engine. It could be a stock rebuild, or every trick race part known to man kind put in it. Doesn't really tell us much about what you have, which leaves us with the unknown of what will work for you.
Getting all the details right is the difference between a pile of parts that drive like crap and you hate the vehicle, and something that works right and is fun to drive. We lack the basic information to fill in the details that make it work right.