Drive a TKO before you buy one. Im not kidding here; I have a lot of customers that don't like getting in and out of 2nd gear. Don't take anyones word for it...try it yourself.
I would put a Richmond 2.88 1st gear ratio T10 in. Or if you plan on making power...an Auto Gear Muncie-based M22z (2.98 1st) 4spd.
I don't know much about the modern richmond T10s in terms of whats included but:
The Auto Gear unit is less than 2grand (not by much); and comes with an improved case, iron midplate, improved extension housing, italian gearset, roller sidecover and your choice of input and output splines.
Take the money you save with either trans and go through the rear end and clean it up. Heres some easy math:
4.11 rear x 2.20 1st Gear (preferred musclecar setup from the 60s) = 9.042 total reduction.
2.88 Richmond 1st x 3.08 rear = 8.87 total reduction.
Auto Gear specific 2.98 1st x 3.08 rear =9.178 total reduction
What this means: Car designers tried to match rear axles with 1st gears to get around a 9:1 total reduction (4.11 x 2.20, 3.73 x 2.50 etc) So if you can match your rear to a 1st gear and keep it around 9:1, you'll be happier.
Now, with a 4spd, your doing a lot less fab work, its lighter, shifts faster and keeping a 3.08 in the back with a 2.80+ 1st will get you better mileage than 3.73s and an OD.
Keep in mind ODs run hotter and louder and the more overdrive, the weaker it gets.
I sell TKO parts...don't break it because parts are hard to find and only come factory direct from Mexico. If you decide to go TKO, and need help identifying what youre looking at...just ask. Same with T56s or TR6060 (T56 Magnum)