It's kind of hard to get away from the engine I have since it did not cost me anything, it has been re-built but with what I understand to be nothing high performance wise on it, I have heard all the horror stories just trying to get other peoples ideas on the engine and how good it was or can be with some minor mods!!! Thanks
I would do an intake, something around a good edelbrock performer , a good cam, with matching springs and a set of headers will wake the motor up well. They are a 2bbl emissions choked out turd until you open it up and let it breath. I'd recomend a comp 268H, I did a mild build with one a few years ago and it worked very well. Ditch all the emissions off the motor and get a good 4bbl carb, something around 600 or so cfm and itll be good to go.
460's are without a doubt a direct bolt in, if its a 4wd chassis you can either spend the big bucks for the L&L mounts or just run a set of mounts off an early 70's 4x4 with a 360, direct bolt on and work great, if its a stick run a flywheel and a clutch off of a 390, internally balanced and accepts a 12in clutch, or if its an auto, just a flexplate and converter for the 460. There are alot more power options with a 460, but if your lookin to make what you got work theres ways to do so fairly easily.
One thing I will say is run quality oil in the 400, they have been notorious for poor oiling systems and your lucky if you can knock over 40psi consistantly. In a perfect world they would have put restrictors in when they did the rebuild. If your going to be running it hard I recomend running a line from the oil galley plug right above the fuel pump up over the intake back to where your oil pressure gauge is behind the intake. These motors were known for poor oiling on the rear bearings, by running this line it solves this issue and gives you more stable oil pressure.