Passon or Tremec TKO 5 speed gear box consideration.

Hey guys, I would appreciate your opinions. My car is a 70 Dart with an A833 4 speed. I have a 3.91 gear in the rear end. Currently at 60 mph the engine is turning 3150 rpm. I plan on keeping this car for a long time and do enjoy driving on longer highway trips. That said I am going to put a 5 speed gear box in it. I am looking at the Passon Performance A855 or the Tremec TKO 5 speed. Does anyone have any insight as to which product will be the simpler one to install. Passon claims that their gear box is a direct bolt in with zero modifications. I have read that the Tremec TKO may need some mods. Also I am in Cleveland Oh. Is there anyone in my area who would be willing to help me with this process once I get the new gearbox? I would be able to pay you for your time/travel expenses.
Thanks in advance for your help.