Trans questions for my '55 3200. Advice needed...

[MotorBike Mike]

So, I'm new to the forum. I've lurked here for a long while and I finally signed up this week.

I've owned my truck for almost 4 years now. It's a 1955 3200 long bed stepside. This isn't my first Chevy truck, but it is my oldest (so far). It currently has a mild-ish 350 against a TH350 against my built 9" with 3.50 gears. I built the rear end a couple of years ago knowing I was going heavy on the motor eventually, and now is the time.

So, I've pretty much made up my mind on engine and components. It'll be a 400 horse 400 small block up against my built 9" with 3.50 gears. The problem is the trans...

My questions are,

Who here has a beefy motor and a 700 trans?
How do you like it?
Is it picky or "finicky"?
Have you broken or had problems with it?
Would you do it again?
Has anyone here used that GearVendors overdrive? Is it worth that price tag?!

Thanks guys!
MotorBike Mike