No Park...bad pawl..or Linkage issue

Alright guys so here's the setup,1972 plymouth duster with 727 tranny with a B&M floor shifter. Yesterday i drove around the block in the duster and as I went to put the thing in park when i got back, I heard this loud clunk and as soon as i let off the brake, the damn car starts rolling backwards. The car will still start, and i can shift into the other gears, but park is gone. I read somewhere that the pin in the tranny for park is called a pawl? Something in the manual about a spacer for the linkage??Anywho, what steps should i check to see if my linkage is just messed up, or if the pawl is bad. I need the version for dummies. Thanks


Bret