318/904 whats it worth

So, a kid at the parts store is ripping a 318 with a 904 out of a 75 dart to jam a 440 in it.
He asked if I was interested in the motor/trans. If I was, it would only be to set it aside and stick it the 71 dart if I ever sold it. Motor and trans seem solid, the motor runs good, but they have 90,000 miles on them. Any Idea the value???
Thanks