hey space cowboy,
if you really want to use that neck to make a cigar box guitar, you can remove the fretboard, shorten the neck and this way you wont need a big box.
otherwise, you better do some planning, figure out where your bridge will go, measure the scale length.
I am sure you will be fine, and I encourage you to build the guitar, but do some planning first.
think and measure twice before you cut it. there's lots of good info here on PG. read lots of stuff and learn all you can.
i don't mean to be rude, im having a hard time writting in english, and I hope you don't misunderstand me.
have fun with your build.