Good idea, Arch!
I decided to keep this breakout rather simple, with just a brief run down on things I have observed with each model's genuine counterpart occuring in the market and how they relate to the reps.
For the 1680's...
-Red font - The red 1680 is still priced somewhat affordably, so seeing one isn't impossible, though most collectors know that the fakes are typically of this dial variation. There are some key details (specifically on the dial) with this one that identify it as a replica; hence even more reason why I like the white font variation better.
-White font - Most plausible, and easier to replicate using a genuine dial (white font dials are easier to find, and less expensive). This one can be made 99% (in my opinion).
For the 1665's...
-DRSD - Most desirable, though more common through 6 dial variations and longer run of production. Again, slight dial descrepancies exist that make it easy to identify as a replica.
-White font - Rarer in terms of actual numbers; shorter production run and a good portion of the white font dials have been swapped out to create DRSD's. This dial variant is not as desired as the DRSD, but is my preferred dial of choice due to it's plausibility.
-SRSD - The rarest of the bunch, though not even closely plausible; case is wrong, dial is wrong, and seeing as how there are very, very few in circulation, this is one that is ridiculous to pull off in terms of credibility.
-COMEX - Along the same lines of the SRSD, this one is so rare and valuable that it is extremely difficult to be convincing. Aside from the fact that the dial and caseback is again, incorrect, this one just says fake at a glance to those who know.
No Dates...
5512 - As a watch that can still be found relatively easily on the market, the 5512 continues to represent a bargain in terms of vintage rolex watches, as it's at a price point that is still relatively affordable.
5513 - The 5513 is a fairly common watch as of current, with an extremely long production run until the late 80's. This watch is also very affordable, and available at a price that signifies a true entry level into the market of vintage Rolex.
Hope this helps!
Best,
R