Sounds like you are 17 and letting all this overwhelm you. You don't have a lot of money but your steering box bolts broke, you would like disc brakes on your front end, you have a tired flathead, you think you may like a 350 Chevy and you would like to switch to an automatic transmission. And to top everything off your car is torn apart and you can not drive it which at 17 is your biggest problem. I can see why you are stuck. Lets take a look at each problem and solve it.
You don't have a lot of money. OK, so do the cheapest things you can so you can get your car back on the road and you can drive your baby. That means fixing your steering box. Drill out the broken bolts and chase the threads and bolt your box back on.
As you have the fenders off and the flathead out now would be a good time to take a look at your front suspension. If you don't have the money for a front suspension conversion put that on the back burner for now. If you have enough money rebuild your stock front end including the brakes.
Engine - your flathead is tired but it is still running. Put it back in and replace the front sheet metal and get your baby back on the road.
Now you have to prioritize your remaining changes. If you want a Chevy 350 and an automatic look for a donor car. You can sell your block and use the money towards the purchase price. Pull the engine and transmission and sell what you can to recoup your purchase price. Make sure to get a good running donor car so you will not have to do any work on the drive train. You can add the speed parts and dress it up later. When you do the swap your ride will not be down that long and you will be able to drive it again until you have enough money for a front suspension swap.
By doing these changes in little steps you will have the use of your car while you save up enough money to do the changes.
As some on the board said. Don't look at your project as one big project but a whole bunch of little ones.
Hope this helps. Good luck with your project.