I worried also when I was a newbie at this. Be patient and save your money. If really worried, buy 2 pairs of 10" drums now. Search posts here and you will see that front rotors were "not avail" and ~$100 used ~5 yrs ago, but now you can buy new for $25 and disk brakes are much rarer parts. If it really comes to it, you can replace the whole rear-end w/ a cut-down Ford 8.8 (Explorer) to get a stronger part w/ disks. Brake parts are common and should be available for decades more. Worst-case, someone will figure how to drill holes to adapt a GM part.
Parts you should worry about are: interior, dash, trim, ... I have even bought several of the now-rare ball & trunnion front drive-shaft "ball joint" (62-65) new on ebay. Don't wait until you must have it, just keep searching for those over a few years. I even found the rare aluminum 4 bbl intake for 64-65 small-block at a good price. What are hard to find are the rare desirable parts (4 spd tranny, Sure-Grip rear, ...). If happy w/ a factory slant six, much less competition.
