How to get rid of understeer in a 1970 340

Ive said it before, these cars were massively undersprung from the factory in the front. They also understeered like crazy. You'd think that the solution to your understeer issues would be a rear sway bar, but that's usually not the case with these cars. You already have HD springs in the rear, which means the rear spring rate is pretty close to correct for a well-handling car.

Judging from the ride height of the front end in your picture, you've probably got a couple things going on. One is that the car is low enough in the front that even with 340 bars you're probably bottoming the suspension out on your bump stops when you're loading it up. Not as much lean, but your suspension isn't working either. The other is that with the rear of the car up in the air like that your rear roll center is pretty high.

Bigger torsion bars in the front, 1"+, should allow you to run that low without bottoming anything. Front and rear sway bars. If your car didn't have a rear sway bar, then you don't have any brackets. Same in the front. Hellwig makes some great bars for these cars, and they won't set you back your first born like the Hotchkis bars will (although they are REALLY nice). If you're really serious about handling better, you'll need to consider lowering the rear of the car as well to get that roll center under control.