My advice is to talk to someone who has experience with BOTH gearboxes and get an unbiased opinion. I will also suggest you try to drive some cars with these in them, as the Richmond and TKO have some driveability quirks that some owners like and some dislike (Richmonds big heavy slow shifting gears and the TKO's 2-3 shift idiosyncrasies).
It sounds like you have your heart set on a 5spd. I can recommend some people who build these things for a living and can give you some insight. Im not trying to be a pitchman here for our product. I don't pay Jon to be here, and I don't mind if you go elsewhere (one of the benefits of not being commissioned).
Send me a private message (not a response in a thread) or an email and I'll give you some contact information for a couple guys. Theres a couple guys who are heavy into the Team Chevelle scene that can give you some insight (one owns a Richmond with extensive mods), I also have a friend in Canada who is intimately familiar with TKOs; along with 3 or 4 other guys who tend to specialize in T5s, T10s, Muncies and Toploaders. Heck if you want the best T56 builders in the country, I'm more than happy to see you get what you'll be happy with.
My response was trying to give you an answer that maximizes the number of factory parts and minimizes the impact on the wallet, while getting the job done.