Hi David H,
I suppose the first question is; Did you have a problem tacking the Nimrod when you had the Bermudan sail on? You've had the boat as a Bermudan for a few years, if I recall and the only thing that has changed is the fitting of the Junk Rig.
If not, then the problem likely lies in the marrying and balance of the sail/mast to the boat, rather than the rudder. The fact that there's no longer a jib to haul the bow around obviously doesn't help either.
But, on the subject of the rudder, I read in a PBO test a few years ago, that the testers found that the tiller loads with the original rudder loaded up as the boat heeled.
The original Wayfarer dinghy rudder apparently had the same problem until Ian Proctor redesigned it. In the original Wayfarer design, the leading edge originally angled back from the vertical and this is what caused the heavy rudder loads.
The redesign seems to have consisted of bringing the leading edge of the rudder blade perpendicular to the water and parallel to the vertical transom. Mine has the redesigned vertical rudder and rudder loads are miniscule going upwind unless the blade has popped up a little, simulating the original design.
I had a quick look on the Sailboatdata website at both the Wayfarer and Nimrod, both designed by Ian Proctor, and on both pages, the original rudder configuration is the same, with the leading edge angling back from the bottom of the rudder stock.
So, if you are thinking of building a new rudder, you might bear the above in mind. But if the boat tacked ok with the Bermudan Rig and original rudder, the problem most likely lies in the Junk Rig marriage or/and maybe needing to use a different technique to that of the Bermudan Rig when tacking.
Sorry I can't be of more help.
David D.
PS. I never did get that Nimrod myself, it was gone when I enquired.