27mm is prbably about right.

With 250 lbs springs 28's work well as they are 254 lbs effective wheel rate. I run my 30's with 350lbs springs. So 220 probably works with 27mm t-bars. Paragon has t-bar spring rate table in the tech sessions. Check that for actual rate. To keep good balance I'd advise running about the same number's front and rear. Stock I think is likw 140 lbs/in front adn 126 lbs/in effective in the rear. So 220 lbs front should need 200 to 225 rear effective.

 

I got coilover plus the torsion delete. found the ability to adjust on the fly is great vs the combo setup. My car needs a repaint so cutting holes and pulling the bars out the side was cost+time effective. also the area I cut was the rough finish, maybe easier to section repaint? alot of track cars go this route. so if your paint is bad the conv might only be a couple hours for full coilover