WRT a rear bar, you might take a look at circle track hardware outlets, where you can often buy modular bits to build your bar--arms, bars of various lengths and diameters, links, and mounts. The rate is determined by the arm length and the diameter of the bar, tubular bars being not a bunch stiffer (of the same diameter and material) than solid ones.

I had a 4000 5+5 street car (wish I still did) and understand your dilemma. I used to trail brake it on offramps and country roads to get the nose pointed in. The toughest issue might well be determining where to mount the bar...

Shocks can make a big difference in the rate that weight transfer happens (though not the ultimate transfer). There is lots of room to play there, even without super-adjustable shocks.

Kirk