Now you are talking about a poly 318? They haven't made those since 1966, then in 1967 they started making the 273's, then 318's and 340's. The polys were a completely different block than the later s/b v-8's.
I've like to hear from a machine shop...I don't think it is possible to bore it out to 4.040.
You could stroke the motor and most likely get 340 inches or more. Read this link.
http://www.moparchat.com/forums/archive/index.php?t-111166.html