I finally found a sedan towbar for the FB (thanks Dave), and will post some learnings here so the next guy doesn't go through the same drama of trying to identify a sedan bar (I hate doing things twice

).
The sedan bar I have looks like the following (excuse my crappy drawing

):

Measurements as follows:
A = 41 1/4"
B = 1 3/4"
D = 5 1/2"
E = 4"
F = 1 3/4"
G = 1 3/4"
H = 1 7/8"
I - 8 1/2"
J = 2 1/2" (tongue is 3" wide - overlaps plate)
K = 1/4" thick
L = 1/2" thick
M = 12"
N = 1 3/4"
O = 1/2"
P = 3"
Q = 1"
R = 4 5/8"
S = 1 7/8"
T = 3/8" thick for large plate and 1/4" for smaller plate
Note that this has separate plates that bolt between the towbar and the bumperbar bolts. The tabs mounted either side of the tongue allow for 3/8" UNF bolts to be put through the rear subframe (requires drilling).
I have also seen this towbar:

on a sedan at Bootleggers, sitting in the same position as my FB sedan one (tucks up behind the rear bumper). Note that the "separate plates" are welded onto the bar itself on this Hayman bar. No dimensions for this one, but they must be very similar to my sedan sketch above.
Bootlegger also had a bar on his panelvan that looks like this:

Dimensions by comparing to my sdean bar as follows:
A = 41 1/4" (same as sedan bar)
B = 1 3/4" (same as sedan bar)
D = 5 3/16" (shorter than sedan)
E = 3 1/2" (shorter than sedan - implies sedan and panelvan tongue are different)
F = 5/8" (very little of the panelvan tongue plate protrudes on the car-side of the the drawbar)
G = 2 3/8" (most of panelvan tongue plate protrudes on the towball side of the drawbar)
H = 1 7/8"(same as sedan bar)
I - 8 1/2" (same as sedan bar)
J = 2 11/16"
K = 1/4" thick
Didn't measure L
M, N, O not applicable - no floorpan mounting tabs on the panelvan bar.
P = 3" (same as sedan bar)
Q = 1" (same as sedan bar)
R = 4 5/8" (same as sedan bar)
S = 1 7/8" (same as sedan bar)
T = 3/8" thick for large plate and 1/4" for smaller plate
Note that this has separate plates like the sedan bar. Looking at the bars my guess is that the panelvan bar will mount up OK to the sedan, but is missing the floorpan mounts (not a great idea). I'm not sure if the sedan bar will mount on the panelvan as I'm not sure how close the tongue-plate sits to the panelvan. Dave mentioned the panelvan bar also protrudes behind the panelvan - anyone got an "installed" photo of a panelvan bar?
Would also like some dimensions on a ute bar please to help make this thread more of a useful reference. I'll measure the bar on my wagon once I drag it out of storage.
I also have a copy of this document, which shows the side rails with some notches and no separate plates:

It refers to FE, and (assuming FE/FC/FB/EK are similar) implies that ute and panelvan are the same, sedan is different and wagon is different again.
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a BB/MD grey motored FED.