Hi Doc Austin,
I don't have a front brake plunger / spring arrangement, part 133D in the 1925 Parts List as I'm also still looking for one. On the veteran forks I have (which are really a basket case), the locators for the bottom arms of the stirrup brake have been removed (as appears to be quite common) - so sorry, no pictures for the stirrup brake in place.
My understanding is that the outer part of 133D is the same as the one used on the crankcase for the exhaust valve lifter. I could be wrong though, but it does look very similar. I will see if the one I have screws into the top of the forks.
The plunger part of the valve lifter is different to the one in the exhaust valve lifter. The brake part has a long rod which connects to the brake stirrup. The Bert Pol brake comes with a short length of what I assume is the correct diameter rod for the plunger, attached to the pull rod of the stirrup brake. (It is used to hold the bits together for transport I suspect?) I can measure that for you. The spring could well be the same for the brake and stirrup brake but I don't have the brake one for comparison.
Hopefully someone else on the forum can help you (and me
) out with some better details / pictures of the spring / plunger part of the veteran front brake.