Torsion bar question.

Well I finally decided to change out my lower control arm bushings and ball joints.

After 2 1/2 hours on the driver side I got it done. The LCA bushing on that side was shot there was only about a 1 inch by 2 inch piece of rubber left, as well as about a handful of rubber powder.

Now I figure I can now do the passenger side in less than half the time.
These things are scary simple! This is the first time I have done any major suspension work. (putting lift kits on jeeps don't count)

Now for the question:
I went ahead and measured the torsion bar. It is at almost 13/16 of an inch (or .8125) so I am guessing .81.

Someone here in town claimed that he has a .85 torsion bar he can sell me.
It Sounds like a good deal but a local mopar guru told me there is no such size and that I should just save my money and buy the bigger ones. (he said .89+)

So would the .81 bar suffice for a high performance 360 mated to an A999 and street 3.23 gears (soon to be 3.55) until the dreaded tax season is over? Or should I replace them before they break? (if they can break)

This a 1974 Plymouth duster by the way. The motor is a 1990 360cu and has 9.7:1 compression with Speed-pro flat-top pistons, 308 heads and Hyd. roller cam at 291/311 dur. and .522/.509 lift.
It also has an upgraded valvetrain, air gap manifold and A999 tranny with TF2 kit in it.

PS. I also have KYB gas-a-just shocks, with the bigger bars I'm thinking it is going to ride like a tank. Bilsteins is another thing for me to get I guess.