if the rear end feels like it’s going to come loose, that is an over-steer condition.
DO NOT stiffen the rear roll resistance (rear spring or rear sway bar). Add more front roll resistance (thicker sway and/or T-bar)
the video below is what happens with too much rear resistance at high speed cornering. My rear sway bar has been disconnected ever since. Might be ok for lower speed handing. But not 70+ mph curves. Especially a dog-leg with a bump accelerating into straightaway.
Every car combination can be different. Make adjustments to what you feel.
My sway bar is .125 diameter, which is much heavier than a stock way bar. Unfortunately, I still have the 13" mini wheels with 185/70 radials all around. The suspension is original in good condition with some replaced parts. Doing the higher speed turns the rear end still has grip but makes me wonder if it will swing out if pushed a little harder.