I agree that the stock set up can be made better, but the biggest drawback to mopar's t-bar suspension is that there are only a few, maybe four that are readily available, five if you score a larger set that some is selling on a message board, stepped up rates available. This severly limits the range of rate adjustment you can utilize.
Of course, there are also very few poeple putting these cars into hard core racing situaitons that require more than the 400# wheel rate of the 1.22 t-bar, but if you did need it, that is the ceiling of wheel rates in a classic mopar. For the GM and Ford camps, that is about mid-range performance levels for racing and they only go up from there. Mopars are in a situation that if you need more wheel rate, you have to go coil over or spend really big dollars on custom shocks to go the big sway bar/soft spring route that the nascar boys are doing now days.