PEDAL TO Z BAR ROD

For 10.5/10.95 scalloped clutches;
1) If you are running a 3-finger clutch;
If when the freeplay is set to ~1inch, AND the pedal can be extended to NOT less that 1" from the floor, AND if this gets you adequate clutch departure of .080 or more, then you have the right pedal box.
Or;
2) If you are running a HD version 3-finger clutch, (like what came in 340/383 cars) then you will need the HD 340/383 pedal-box, which has
a) the long-ratio pedal, to increase departure, and
b) it has a bigger heavier overcenter spring to deal with the extra pedal-effort, and
c) it has the bracket covering the overcenter spring,to help the pedal-box deal with the HD spring.
But;
3) If you are running a diaphragm clutch, then;
a) the HD overcenter spring will have to be removed, to prevent the clutch from sticking to the floor at high-rpm, and
b) with the spring gone, the bracket is no longer needed, and
c) the diaphragm will work with the 6-cylinder short-ratio pedal, albeit with a lil more pedal travel, which then
d) makes which pedal-box you have, a non-issue
I think that's right.
4) no matter what you run, the TO fork has to park near the front of the window in the BH, AND the adjuster rod that goes from there to the Z-bar has to end up about parallel to the road in side-view, and about parallel to the centerline of the car in plan-view. If it is not, then you will have issues in both effort and departure.
Not having it set this way, has troubled more than a few hot-rodders, because of the several possible combinations of various parts;
I know, for 67 up A-bodies, there are at least;
2 pedal boxs, with 2 possibly 3 springs, and with or without the bracket
3 aluminum SBM bellhousings,
2 Z-bars,
3 inner Z-bar pivots,
2 or 3 forks,
3 fork pivots
2 adjuster rods and
2 TO bearing assemblies.
By the math, this comes to about 2600 ways to screw up.

In my car I have a 10.5 CenterForce diaphragm, and it runs the 340 pedal-box, with no overcenter spring and no bracket. I get adequate departure with the pedal extended to slightly more than half-way, at the very modest freeplay adjustment I use.
At some point in time, I added a junk-box overcenter spring, that IDK what it came out of, to help pull the pedal back up to the dash-stopper. Yes, I do, have TTI headers, and yes I did run into interference. The Z-bar needed a lil offset, and the headers had to be "clearanced", cuz I was not messing with the perfect-functioning clutch. AND,
I re-engineered the adjuster rod, for ease of adjustment access ..... which is a fancy way of saying, that I got rid of the interference loc-nut and got rid of the subsequently required double-nut locking system. Instead, I put one nut on the radiator side of the metal swivel, then a tube spacer and a second nut on the back-end. The spacer pushes the back-end nut out to the back for ease of access, cuz the header is right there. On the very end, I drilled a hole to receive a hairpin, cuz one time that back-end nut came loose and disappeared, along with the spacer. This allowed the freeplay to change. Eventually the hairpin disappeared so I installed a soft cotterpin. With the system now working properly, I use a socket and extension to loosen the Back-nut, spin the Front-nut down a turn or two, and lock it back up. and yes this can be done with hot-headers. Because this only takes a few minutes, I run a very small freeplay; just enough to keep the TO bearing off the Diaphragm for the summer.