Need a plan - component selection for restoring 68 340 that runs on 91 oct

Stock build...Just duplicate the factory specs including the cam,the info is widely available.
Use a sealed power C28P, a stock replacement cast piston that sits a hair below the deck.
Classic Exhaust out of Ohio make a stock exhaust system (very economical). Make sure you use the the stock replacement mufflers they provide,not their hi performance muffler. It will be reasonably quiet until you step on it but sounds just like it did in 1968 and you will hear the moan of the unsilenced air cleaner.
In an A body with stock 14" tires and 3.23 gears it will pull hard to past highway speeds and probably get 20 plus rpm driven sensibly!.