Thanks for the kind words.
Now, on to your question.
This is of course a matter of opinion, but here's my line of reasoning:
For the "older" R type ships I used the generic metal CA (ADB stock #0204), modified by drilling into the nacelle caps and placing the ends of metal sewing pins in them. I did this because the Zocchi mini is less forgiving if you mess up, since plastic does not deform as much as metal and the saucer is less detailed, and the older ships are supposed to be less "detailed" (plus and I have a stash of about 6 Zocchi CAs around in case I want to make "newer" cruisers like my model of the Potemkin). The R type ships were upgraded to the same stats as the Constitution class, but were still noticeably different (like having a smaller bridge as pointed out by Admiral Williams in the story "Encounter at Denebola" from CL#5), so I definitely wanted to use a different model on the table.
I know that others including Djdood have done the opposite of me and used the Zocchi plastic CA for the older ships, quite possibly because the model is older and it is no longer available, and generally people aren't going to be making models of tons of "older" ships. (Although, since module Y2 is coming out soon....maybe I'll get into another project.....

)
Now, to make each of the CA, CA+, CAR, and CAR+, that involves using epoxy for extra phasers (the metal CA comes as a CAR+, having the extra rear phasers and the underside 360 ones, while the Zocchi plastic ship is just a CA with no rear or 360 phasers), and adding drone racks either by decal or paint, your option. I chose to use decals and thus the CA+ and CAR+ both have a drone rack.