front sway bar upgrade
 

My '71T has the stock 15mm through the body sway bar in the front.

Are there any larger bars, factory or aftermarket, that will work with the stock hardware?

There is a factory 18mm front bar from the early Turbos that will work fine with your hardware. I got one for $75 used and put it on my early "S". However, you also need to upgrade your rear bar at the same time, so as not to upset the handling balance. Luckily, all the '74-'77 911S models had an 18mm rear bar which will fit and can be found cheaply at junk yards (the early Turbo rear bar will not work because of a bend around the 930 trans.)

Most aftermarket bars will come with their own hardware. About the only thing you use from the factory setup is the U-Clip on the A-arm.

TT

I just instaled a aet of 19 mm Weltmeister bars in my '73. Mt car had the thru body holes already drilled and the u tabs for the front bar so it was a piece of cake. For the rear bar, I had no mounts at all and used the kits provided by Weltmeister. Ecpet for a lack of instructions, it was pretty painless to install. They also offer bars in larger diameter.

An AutoX pal uses Charlie Bars in his P-car. Silimiar setup but appears to be a slightly better quality.

I would suggest that whatever you choose, go with adjustable ones.