If the tr6 handbrake is anything like the Spitfire handbrake...
I will try to explain how I did mine.
Pull the clevis pin out that holds the cable assembly to the handle.
Handle out of the car, upside down on the bench for the first part.
Install the cam dr5 and it's pivot dr6. Making sure the teeth are toward the large end of the handle, don't ask me why I make this point.
Slide the button and spring assembly dr3/4 into the handle with the open side of the loop facing toward you. This loop goes over the top of the cam. You need to accomplish two things here, getting the button centered to go into the handle, and rotate the cam into the half circle as the assembly comes into position.
Another way would be to install the button/spring/actuator wire assembly first, held in with a strip of duct tape, and then put the cam in, with it's rounded top nestling into the half circle, and then put the cam pivot in.
There is no direct connection between the cam and the button assembly, the wire just lays on top of the cam, held there by the fact that there is no room inside the handle for it to slip off the cam. This might be the point that is the confusion.
Now comes the part that you can't do on Sunday because it takes some cussing to get it done.
I used a strip of duct tape to hold the button in until the whole thing was safely installed in the car.
There is a little "wing" on the bottom of the ratchet assembly, dr7, that fits over a corresponding tang of sheetmetel sticking out of the handbrake mount on the car.
You must put the ratchet in the handle, start to slide the handle into position, put the wing over the tang, rotate the ratchet into position in the handle and put the pivot clevis into the handle capturing the ratchet.
I found it helpful to coerce an unwilling accomplice to put a loose fitting pin punch (a 1/4 inch drive extension would work too) in the pivot of the handle to hold everything sort of where it belonged while I got the pivot pin ready.
The ratchet "floats", captured by the pivot pin and sheet metel tang, resumably so that there is always a little "slack" in the cables so the cam doesn't bind on the ratchet.
Remove the duct tape installed in the previous step.
Once the pivot pin is installed, the cable clevis can be put back on the handle.
and tada, one functioning parking brake. Piece of cake.
Buck up Dale, the pictures show a car that would be welcome at any gathering of LBC's. You have something to be proud of there. Don't let your discouragement over this one aggravation drag your whole view of your hobby down.
If I may be so bold, from what I see in some of your posts, perhaps your percieved machanical ability causes you to replace parts that are not necessarily needing to be replaced. Notice that I said "percieved" because no one, no one, gets to the point you are at, especially with a car that was as buggered as you say this on WAS, without some innate mechanical ability.