If up grading, use either a drum master cylinder if you are using drum brakes of a drum/disc and a proportioning valve master cylinder. Make sure the components match.
If it's street car, you won't notice the HP loss. Running the manifolds versus headers would be my choice because unless you buy the TTI headers, you will be
"clearancing" them as you mentioned.
Go back to the basic tune and begin making ONE change at a time to see how it affects the engine, how it runs out and how it drives. Making wholesale multiple changes will bite you in the *** because you don't know which change effected what.
I'm going to paint mine because the original owner put rattle can clear on them and it turned yellow. I've tried many solvents and nothing will remove it.
Welcome from Texas, if you can afford the car buy it. It will give you untold enjoyment tooling around Europe in an American vehicle. When my wife and I were on Poland Christmas a year ago, I saw only one American car in the 16 days we were there.
Doc, if you bought all of the inventory you could probably make enough of a profit over a period of time to finance your builds. But, you have to be willing to take the time to either swap meet the stuff or post it here and on market place. This might be a great learning and teaching curve for...