Thiokol 604 Brake System Rebuild.

[modifier]

I posted this in the Restoration section but maybe it would be better here? Is there a dedicated Thiokol forum?

I'm getting parts together to rebuild my brake system on my 66 604.
There is 1 original brake slave and a replacement that looks pretty new. I was told it should be an Enerpac RCH121. Grangers has an Enerpack RCH121-H and it's about $100 less in price. Both are expensive and before I ordered anything I wanted to see what was in the 604. Turns out it has the RCH121-H in it. The specs are close but not the same. The main differences are the 121 has a stroke of 1.63in and the 121-H is 2in. Also the working pressure is the same on both, 12 tons, but the max pressure on the 121 is 13.8s ton while the 121-H is only 12 tons.
Does anyone know anything about any of this? Also are all 600 series use the same slave?

Also I had to loosen the band clamp and move it aside to see the part number on the one in the 604 and even with it loose the RCH121-H still felt firmly in place. That clamp can't be all that holds it from moving with that much force. How else is it attached and how do I remove it?

I tried to upload a jpg if the factory 121 photo but "the uploaded file was not an image as expected" It's small so I don't understand that.

Here are pics of the unit in the cat. The other one looks to be original.