either will fit with your column shift, although you may need to alter the linkage slightly. tti offers a full length and a shorty-- i know you have to mod the linkage on the shorty, but it's not a big deal.
both sell a quality product, however you can call tti on the phone if you have a problem.
additionally, tti sells a complete exhaust system from the headers back.
[URL][URL]https://www.ttiexhaust.com/index.htm[/URL][/URL]
pros: it's cheaper
cons: it's loud, you may also get drone at specific speed/rpm
there are several companies that sell tail pipes (the part that goes from the muffler up and over the rear axle and to the bumper) specifically designed for 67~69 darts.
a competent shop should be able to handle an install if you show with parts.
part of the benefit of a complete system such as TTI is that it comes with everything you need to do the install yourself. the connections are slip fit with clamps so you just bolt everything together and you're ready to party.
there are other companies that make complete kits (pypes, hooker blackheart) that are similar and can be installed at home, i know a few the fit is a little more fiddly than others but it's all doable.