6" wheels at the front, 7" wheels on the rear, redline tires; I don't think the owner is interested in 'good' handling that much, so anything bigger than 1" probably won't be chosen anyway.

I've got 1" torsion bars on my '73 Dart, upgraded from 0.870 bars.
But wouldn't be opposed to upsize even further to 1.06 or more.
I believe 1" bars should've been standard on A-bodies to begin with.

(A-body bars are shorter than B-body, so they are firmer than 1" B-body bars)

We have 1" torsion bars on our 70 RR with a stroked 400 (452) with Edelbrock heads and a Weiand tunnel ram. I do not feel they are too harsh. Have been thinking adjustable shocks stiff on compression a little softer on rebound will go a long way to helping our oil pan survive (road race pan and have managed to dent it, of course, the car was stuck on top of a large rock at the time...). With your description of your friend's car with all iron engine get the spring rate up, go 1". I think our's are Mopar Performance.

My '68 Hemi 4-speed RR had its stock bars & springs. No problem lifting the nose on acceleration, and though I never considered it or drove it like a canyon carver, it did handle pretty decently (I have another car for that purpose). Main problem was traction: at 540 dyno'd HP, 295/50 Radial T/As on 15x8s were useless until 3rd gear. I ran 265/50 fronts on 15x8s.
A set of M&H DOTs were needed to accelerate the thing under full throttle.

Topside. What was the stock bar diameter?

And fellas, which company would y'all consider to get the T's from? Mopar, Firm Feel, Hutchinson, etc.

Thank you guys. This stuff is black magic and rocket science all in one.LOL.

I don't recall the measurement, it was a long time ago when I was verifying the car; but they were stock Hemi bars, which IIRC was .920...sway bar was also stock, BTW. I did lower the nose a little but not too much as it had a pretty big Milodon pan.

My combo fwiw,...

70 RR 475" Hemi iron block, Al head, tti 2&1/8", 4spd.
.920 bars, & Bilstiens all around.

Two different friends, one with a 69 Hemi 4spd Superbee, other with a 70 V code 4spd Superbee, have both ridden in mine and commented "it rides like a Cadillac".

So it's time to improve?
I would be insulted with comments like that

I have the Mopar 0.96" T-bar on my Charger and Coronet. They have a good ride on the street. The Charger has the old KYB gas shocks, and PST sway bars, poly bushings, and stiffer rear springs. The ride is about like most new cars, maybe a bit on the firm side, but not harsh.
The Coronet Convertible (a bit heavier than the Charger) has the RCD Bilstein shocks, Mopar replacement HP rear springs, and stock R/T front sway bar. The car rides smoother, almost soft, most likely the difference in shocks and having rubber bushings. It could use larger sway bars in my opinion.
The 0.96" bar is not great for drag racing. If you want the front end to lift at the track, the smaller bars would be better. Also, I think the 0.96" bar is the largest that is still indexed Left and Right? I think the 1" and larger bars have the same index and can be used on either side of the car?

The Hotchkis 1.03 bars that I have are labeled L and R. I haven't installed them yet maybe next weekend if I can get the K frame ready and painted today I can install them next weekend. I also have a set of 0.96 T bars new in the box and the stock 0.92 set. I always thought that the stock bars were to soft.

One thing that came to me after my suspension upgrades;

Wrong (cheap) shocks can make a ride 'harsh'.
Thicker torsion bars just make a ride 'firm'.

Shocks are best to be matched to the torsion bars.
Thicker bars need better performing shocks to handle them.

I still use the factory T-bars in my 63. It was a 383 car and going by the chart Dwayne posted they are .900. I have the CE 90/10 front shocks also which works fine on the street. I have no complaints as my car is mostly street and it handles fine and works fine at the track . Ron

I went with the 1.15 bars from bergman, will probably go with the viking shocks down th road. tim