It's been awhile since I bought them so I can't remember all the specs off the top of my head. I remember the front segment was a little different then stock A-body springs but it isn't much. IIRC it's only about 1/4" difference? I have them installed on my 68 right now while I wait to get into the paint shop. I've got a set of old Rallye's on it and they look fine in the wheelwell.
Oval track springs front segment is 20.5", so half inch longer than A body/SS springs but shorter than B/E springs. The typical Mopar show fender tag number cruncher will probably notice something isn't quite right in the rear wheel well, but may not know what. In my Challenger I used the 2" longer SS hangers, so in combination with the oval track front segment, I have actually pushed the rear axle back half an inch from stock. I've had a couple people notice it and ask if I've relocated the axle.
I guess this means that the front /6 T bars need to go, A factory 340 or 318 leaf spring is acceptable?
Absolutely get rid of the slant 6 bars. Probably want something like .94, 1.0, or 1.06 depending on how big a sway bar and how aggressively you want to run corners. With those, add a 1.125" solid or 1.25: hollow bar and they may be a nice match for a set of 340 leafs.
Is there any info if I start researching the Trans AM cars of the 70's?
The first couple of years of the TA series had several '65 D Darts prepped specifically for road racing. In fact, the very first race in the series was won by the '65 Dart of Bob Tulius in the over 2 liter class. The Darts were competitive through 66 and into 67 before the Ford and Chevy pony cars began to dominate. I'd imagine you could dredge up some detailed info on them if you look.