Calvert Mono Split Leaf Springs

Wonder if anyone can help me. I have Mancini XHD springs and have serious spring wrap issues. I solved the problem about 85% by putting 4 clamps on front of spring and raising the pinion snubber. Must be a weak main spring. I talked to Calvert today and they suggested their split mono leaf spring that has a 225 lb. spring rate compared to about 110 on the Mancini's. This is a four speed 383 big block 1968 Dart. The spring wrap occurred when pulling out on a hill or releasing the clutch normally. The car would shake horribly. At first I thought it was clutch chatter, but after talking to a long time Mopar racer, he said immediately that I had a weak main. In fact he said they have tossed Mopar Super Stock springs recently because they had weak mains. Brand new as well. I clamped the springs and raised the snubber and the problem is much better, but not right. I just want to make sure these Calverts are good. I plan on running them without Caltracs bars and just the adj. snubber. Has anyone done this with a four speed big block?