Factory ride height?
Mopar defined front "ride height" by measuring two points on the lower control arm compared to the ground -- essentially, this was the angle of the lower control arm, which is controlled by the torsion bar adjuster bolt.
Measuring any part of the body or frame to the ground is dependent on your wheel and tire combination, and even the tire pressure and temperature, so it wouldn't be a consistent measurement.
I don't quite understand the bit about the 1.03 torsion bars "lowering" your car. Since they have a stiffer rate, I would assume they would raise the front of the car -- then you would have to use the adjuster bolt to lower the front to where you wanted it. This would be a different number of turns than the original t-bars required.
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Measuring from body parts is of no use, as suspension has to be set relative to its components, in relation to floor. Body parts are not consistently mounted, and are aligned to mate with their neighbor, not suspension parts. These cars dont have close build tolerances.
Per Factory Service manual:
Front suspension heights must be held to specification for a satisfactory ride, correct appearance (this subjective to todays eye), proper front wheel alignment and reduced tire wear,
First vehicle has to have full tank of fuel, no passengers, no luggage in trunk excepting spare tire & jack, properly inflated tires, and on sitting on level floor.
Clean all crud from lowest portion of steering knuckle arm, and height adjustment blades directly below lower control arm inner pivots.
Jounce front of vehicle several times releasing it on a downward motion.
Measure from lowest point of adjusting blade to floor (measurement A), and from lowest point of steering knuckle arm to floor (measurement B); measure only one side at a time.
Subtract distance A from B and adjust height by big bolt in center of LCA adjusting as necessary until A-B= 2 ½ +/- 1/8th inch. Per 1967 A Body height spec for both standard & HD suspension; I suspect it is the same for a 1968 & 69 A bodies.
After every adjustment jounce front end before remeasuring. Both sides should be measured even though one side was adjusted. Adjust other side.
Ping pong left to right making adjustments until each side is within 1/8th inch of the other.
Im not fluent in 69 340 rear suspension, but suspect it is identical to S Cuda set-up which I believe used a six lief factory ride height rear spring. Even though a six lief spring was used, it was not significantly stiffer than stock springs, but provided better axel control under hard acceleration.
Your choice of one inch torsion bars is a good one; these cars left the factory with mushy low spring rates on the front end compared to todays cars. GM and Fords suspensions were even sloppier than Mopars in the day providing almost no suspension control, they were simply dreadful wallowing hogs.
I have fitted six lief stock ride height rear springs to My Dart rag top with an 8 3/4th inch rear, with 0.940 torsion bars all at factory ride height, and car handles neutrally with a well behaved rear axle.
Rear spring ride height changes in one inch increments are available if one desires a slight lift of rear end. As rear of an A body over stock ride height increases, the more tail happy (tendency to over steer) it will become.
Call Spring N Things
ESPO for the details, A body rear springs are not listed on their site: http://www.springsnthings.com/
