I've been thinking about the
Bonaventure. It's no secret I'm not a fan of the design as is, but the vessel is prominantly mentioned in the episode so it cannot really be ignored (unless one envisions a live-action version of the episode where the vessel is never mentioned). That said my view is to try to come up with something more plausible that fits with what we do know from TOS and supports Scotty's refrences.
Scotty said the ship was the first ship with warp drive and it disappeared 150 years earlier. Okay, technically Zefram Cochrane's ship was
the first Earth ship with a space warp drive. But maybe the
Bonaventure was the first Earth ship with a more familiar warp drive system although by TOS era standards it was still a rather primitive setup and thus not conflicting with Spock's assertion in "Balance Of Terror" that Earth ships a century prior to TOS were "primitive" vessels (primitive being a relative term).
So that leads one into speculation as to what TOS might have come up with to depict a 150+ year old starship. I think it's reasonable to assume it wouldn't have looked remotely like the 23rd century
Enterprise. And I am not going to use ENT designs as a reference point since those wouldn't have existed back in the day as reference anyway. Different creative teams from different eras with different objectives and reference points.
I might have something of a starting point since I have taken a stab at designing early 22nd century starships by extrapolating from some of Matt Jeffereies early conecpt sketches when he was working his way toward a final design for the
Enterprise.
Although not specifically dated this was my take on an early to mid 22nd starship. Yes, it has three nacelles, but I reasoned this was an era (late 21st to mid 22nd) of experimentation when different things were tried in search of an optimal arrangement and configuration. I envision the
Bonaventure looking smaller and more rudimentary than this.