I just installed uprated srings on my TR4A yesterday. I am very pleased with the results. The ride is good as is the handling. It does sit a bit higher then factory springs though, with the uprated springs installed.
The specs on the springs I used were:
free length - 11.125"
outside diametre - 3.875"
wire diametre - .559"
After the install the wheel arch height came out to 28" for the rear and 27.875 for the front. The frame sat 7.5" off the ground in the rear and 6" off in the front.
I hope this helps.