I have an old 1990 rigid Kona MTB as a sort of hack. It is Gorgeous. I value it way above its nominal worth, which is probably about half of less than nothing.
I wouldn't bother with paint or powder coating... Put in a cheap BB (less than £20). Even if you need to buy the tools, it won't be another £20. Headset you can get for about a tenner and no special tools needed apart from a mallet and a good stick.
Stick the seat post in a vice and turn the frame, or just ride it at that height... if it's your bike it'll be right for you without adjustment.
Glory in the love of an old Kona and enjoy having a bike that is awesome but looks so shitty that no-one will steal it.
This isn't one option of many; it is the only thing you can do - and you know it.