GM 350 auto trans locked up???????????????

I have a LOKAR floor shift and the four button head 5/16 x 3/8 screws fell out. (the four that are located within the curved slot). This of course through alignment of the gear selector off. I purchased four more from Lokar along with the safety plug to set the safety switch in the proper position. I placed the shifter in park and started the car. Now the problem... the car wants to move foreword in any position I place the shifter in (except park). I cannot find the neutral position and reverse. In addition, if I push the car back and forth the car rolls very easy as if the car is in neutral regardless what position I place the selector in. (it's a 32 roadster) except in park. I have to apply the brakes hard when running in order to keep the car from moving foreword.
I'm only guessing that somehow the transmission is locked in some gear but this makes no sense the car will stand still in the park position. I should add that when I try different gears the car starts to run rough and acts like it wants to die. I did not touch or remove the side linkage at any time. The 350 trans. only has on shift lever on the side so I can't understand how the transmission could have crossed with another gear like the older ford transmissions that had two side levers that you could get jammed. I have tried loosening the four button heads and changing the position of the "banana bracket" but this does not change anything..... any ideas?

Ok, looks like I found my problem. The S hook came off the rooster comb plate because the 11/16" nut became loose and the rooster comb loosened up. Now, how do I tighten it? An 11/16" open end wrench will not fit in the narrow space. Do I grind down the side of my wrench? Also I noticed that there is no lock washer behind the nut. What will keep it from just loosening up again?