I think the OP is talking about the idea of removing the 6 springs from the main drive axles, so that the coupled wheels don't have any movement....(at least that's the way I read it).
I'd be a bit scared of doing that....you'd have to add packing to the top side of the journal to replace the "air gap" that now exists where the springs used to "live".
I agree that the 4 things to address are:
1) Front bogie spring....reduce/remove spring and add some lead weight
2) Rear bogie.....make sure it can ride okay without lifting the rear drivers. This may require "surgery".
3) Fall plate....make sure it can move enough so that it doesn't affect the loco-to-tender relationship. It needs to be able to swing freely.
4) Add as much extra weight to the boiler/firebox/cab/chassis as possible
That was my thought, I have other engines with no springing (or springs that are that hard they might as well not be there) with no operating problems.
To address your points:-
1) Haven't looked at the front bogie spring on either mine or the mates, so will do.
2) Rear bogie has been adjusted and isn't the problem.
3) The fall plate on both mine and the mates snapped off while endeavouring to insert that damn plug, which by the way will never ever ever ever be removed, what a cow of a thing. So no footplate to create an issue.
4) When I noticed the front drivers lifting we hung a very substantial lead weight over the front of the engine, it came to a wheel slipping halt at exactly the same place! with the front drivers still lifting from the rail head.
The track does dip up a little in the area thus increasing the grade, I thought it might be creating a hump past that point that was letting the front drivers lift but it doesn't appear so.
Before I return to the railway I will make a couple of test platforms that I can use to check the hump and dip in this area, I have made a couple that is used on the club garden railway, they being a couple of flat platforms with a pair of bogies under each, you just push them around and not the ride height differences between the two platforms, the platforms should obviously be the same height, if you put a substantial overhang on them you can see variations very easily, on well laid track there should be very little variation.
So plenty of testing to do, I was feeling the water to see if others have been experiencing problems and what their solution may have been, removing the springs will be a last resort, thanks for your responces, feel free to keep the conversation going.