I'd reccomend saving the original engine in a bag and building another 340 or even a 360. Add a stroker crank (night and day difference in power and looks and sounds totally stock). If you want to save a few bucks you can use the original heads, intake, carb, accessories, etc. on the new engine and just save the numbers shortblock. Two reasons I reccomend this. #1 you will always have a numbers matching car (which is exceedingly rare with 340 stick 71 Dusters) and #2 you can bag on it guilt free when it's done. Nobody will know it's not the original engine unless you tell them, they all look the same on the outside.

*I hope you are getting a bunch of pics of your forward radiator support blackout brfore getting it stripped? From all angles if you haven't, not much good info on that.