Factory Surge Brake Specs

My '86 CC trailer did not come with the factory option of surge brakes so I'm converting over. I've noticed that the new Atwood couplers are manual lock out with a knob to activate it. I've never seen that knob on my dad's '88 trailer with surge brakes. Does anyone know if those were free-backing brakes, or is there something I'm missing? Regardless, I'll utilize the uni-servo option for my setup.

Also, can someone confirm that the brake hub size is 12x2?

The Atwood coupler that I'm looking at, which is identical to the factory ones, is intended for drum brakes and has a manual lock out. It still disengages the brake in reverse even though it's not disc brakes.

Free-backing drum brakes wouldn't need a lock out, but uni-servo still would.

Atwood sells disc-specific couplers of the same style. Drum brakes can utilize reverse braking.

I'm simply trying to recreate the factory system as close as possible. I'm getting an Atwood coupler since the that's what CC used in the 80s. Perhaps the older couplers didn't have the lock out feature and utilized free-backing brakes, but that's what I'm trying to figure out. If someone can confirm that, I'll use free-backing brakes and not use the lock out feature.

The free-backing brakes are the same cost as the uni-servo where I'm looking to buy them. The rest of the system is the same. I just want to know what the factory did.

My current truck isn't as beefy as my old one and definitely needs a bit of extra help braking when towing. Since I can convert over to surge brakes for less than $400, I think that's money well spent when I have my family in the truck and my pride and joy and in tow.

Awesome, thanks Hollywood!