63 Dodge Dart newcomer questions/advice

Welcome to the board. That's a very cool looking 63 Dart. Look solid enough, but may need a few things like you said the driveshaft and maybe some help with the springs in the back end. The front bumper looks great. Although it is missing the headlight trim rings oh, but you can make do without them. I love the color and I love the VP decal on the lower right front fender. I think you are to stick with the Slant six and get it running and driving with it and the small 9 inch brakes. Once you go with the 318 V8, you should upgrade to at least 10 inch brakes or possibly discs up front. Like previously said you're going to have to modify the windshield wiper motor area of the firewall, but I have done that several times when putting a V8 into a 63 A body. Some people cut that area out and weld in a later year area, but I choose just to carefully move that area backwards enough so that the distributor fits. Forget changing the K frame, your current K frame will accommodate a V8 just like the 64 65 and 66 has. Also you may want to upgrade two V8 torsion bars as I am sure 55 plus year old slant 6 torsion bars have their limit as to how far they can be cranked up to hold the extra weight of a V8. You'd have to find a V8 radiator and V8 motor mounts not to mention the early V8 exhaust manifolds to do the swap. If you can find a V8 parts car with everything in it then that would be the best thing to do, but for now get your slant 6 going and enjoy it. By the way, the only way you can use the push-button transmission with a V8 is using the 64 V8 transmission. 65 is a little different but you can use it.
I would find a ball and trunnion drive shaft for an early Dart locally, not a Valiant as the drive shaft is shorter. Fix your Springs in the back if needed, and put some decent wheels and tires on it and go cruising.
Good luck with it.