what does it take to swap a big block in a duster ?

I bought a 73 duster from a friend with a 383 and 727 tranny. The k frame is a spool mount. With the motor mounted my tranny doesn't line up with the tranny mount. The drive shaft seems to go into the tranny far enough but the holes in the tranny are about an inch to far forward to bolt to the mount. Anyone have anyn ideas why???