Basic /6 costs for upgrades to a 70 Dart

There are many here more expert, but since nobody yet answered, I'll answer from what I have read:
1. Motor mounts - Schumacher, etc. Have heard of a ~$100 set. Other option is to change the K-frame.
2. Transmission is different for V-8. At least $100 used.
3. The driveshaft may also change.
4. Most people change the 7.25" rear-end to 8.75", especially if racing. Then #3 for sure. Maybe $300.
5. If #4, most people change to the later bolt pattern (called BBP, 4.5" circle). Then you must change the front hubs to match or carry 2 spares. Set of 4 wheels & tires, $400+
6. With #5, most people install front disk brakes. $100 junkyard, $700 after-market.
7. V-8 requires a different steering link to clear the engine. $50+.

If you want a car to drive, consider upgrading the Slant Six. I would say people have as much fun and pride with that and will drive it more with teh better mileage. You could put in a turbo for maybe the same price, though you have to be a good welder or know one. To me, the attraction of the car hobby is being a little unique. How many times do you go to a car show and see rows of Camaros or Chevelles with a 350 and Edelbrock carb. All the engine bays look like clones. I like to see the cars where somebody had to think and design a solution.