73 GOLD DUSTER

I say, in general 73-6 will take a back seat price wise to the 70-2, that is the market. Same with any Mopar built after 71, just fact. There are people that might like the later duster better. BUT he will spend $ based on what is considered fair market value. The slant? many people love them, as I, but again the market for the slant tend to low ish. Most people but the slant duster to do a v8 swap later, some will enjoy the slant and decide to keep it!
You are asking can be buy this 73 slant duster, do some work on it and sell later and get your $ back or make a profit? I will say this after 30 odd years in the hobby, the more $ I spend ( yes I do all the work), the harder it is to get my $ back! But you doing work that NO seller will find fault with, will greatly help the sell it. Example: IF you do paint and body, take pics of every step, save all receipts, have a perfect topcoat on a effect straight body. If not perfect you need to sell to a guy that wants a driver quality only. NO you can 't pay a shop to do paint work on a cheaper car especially.
Rememeber, basically it costs (almost) NO more to restore a 69 383 Roadrunner than a 73 slant duster, other than the initial cost of the project!