Some progression and added detail...with more to come. There are bits to be added to the landing struts and some overall hull detail. I made one small correction since the starbase mentioned in "Slaver Weapon" is Starbase 25 rather than 27.
One thing to note is that I cannot think of a way to add impulse engines to this without really changing it. Of course when this was first drawn by the animators it's likely no thought was given to this. I would be curious to know if the TAS designs were something they just thought of an the spot or if someone had actually sketched out ideas for them. It would be very interesting to see concept sketches of the new ship designs seen in TAS as well as for the aliens too.
Anyway I'm thinking of taking a page from TMP's shuttlecraft and having the ship able to go sublight by antigravity drive. That would be that object you can just partly see under the main hull behind the support struts. I thought I could put it there since it isn't an area we got a good look at onscreen except perhaps for one quick shot.
I must say I prefer the cleaner look of the nacelles without the bits I added on top, but there is something like that on the original version although onscreen they look too much the the Enterprise's
nacelles and so I simplified them for what is supposed to be a high-speed shuttlecraft.
I've tried to keep the essential concept of the original while shortening it in length and softening some of the sharp lines and angularity of it. It also won't be as spacious inside as what we saw onscreen. I solved the forward viewport sightline problem by envisioning the forward flight control area as a sort of elevated cockpit where you have to step up slightly from the aft area into a forward section where you cannot stand upright. Consequently this allows me some extra space under the deck for mechanicals. While thinking this through I learned from my drawing of the Class F and wanted to allow between hulls space for the craft's guts. The only place about the hull where there'll be no room for mechanicals will be the main viewport.