In a 1967 the TH400 was the only three speed automatic available at the time (the TH350 wasn't introduced until 1969). If you have the corect cross-member mounting points you need to just bolt it in and shorten your drive shaft about two inches.
In 1967 your car, if it had an automatic, it would have used a PowerGlide two speed (which is basically a broken TH350 and I say that because the low range in a PG is the same ratio as second gear in a TH350). So your not being able to get out of park could be from some one not using the correct linkage to reach first gear, and the rest of your problem just being out of adjustment.
Not having fluid in an automatic or a manual tranny and attempting to drive it will destroy either type of transmission though.