v-8 replacing a in-line 6

[Brock]

My new purchase ('68 stepside) has an in-line 6, and a 3-on-the-tree. Don't know if either works. I popped the hood to let my Dad take a look at it, he's pushing 80 and was a mechanic back when this thing was new. Even with a touch of alzheimer's he declared what the motor was and that it would take some modifying to make a SB V-8 (307 for now 327 eventually...with a 700r4 tranny) work. Not that I'm doubting my Dad, but just curious how much will need to be done to get it going? I am a mechanical idiot but I can figure it out eventually....sometimes with help.