My 64 Dart Vert Project

Hi guys , I am new at this forum stuff so first I wanted to comment on DART4FORTE'S 64 resto, MAN WHAT A GREAT JOB YOU DID ON THAT CAR, IT'S AN ART TO GETTING THINGS DONE RIGHT THE FIRST TIME AND LIKE GOOD ART IT SURE IS BEAUTIFUL TO LOOK AT!!!
but not to the A bodies, I just finished AND HAD TO SELL my 69 cuda restoration, it went from a stock 318 purchased for a GQ photoshoot) . After the shoot i had an idea to add a reverse spin supercharger tucked away by the radiator and a custom built airbox (sleeper style) using a beefed up original air cleaner lid, to a 360, .60 over aluminum racing heads, roller rockers, 518 manual shift overdrive and a dual fuel (propane+ pump gas) 200 mile an hour autobahn cruiser.
now I just acquired a 64 dart convertible with a slant six and a 904 pushbutton tranny, yesterday while driving the trans locked up temporarily when it shifted to second gear it almost felt like the trans went from first to reverse then back to first???
Does anyone have any idea what could have caused this problem? Prior to this new situation the car shifted fine? I bought a used 904 with a recent rebuilt from a 73 duster and when i got it home and the car on stands I realized that the shifting mechanism will not work, Any help resolving this would be greatly appreciated