Fit the new manifold and twin carbs, then get the booster rebuilt and fitted. Get the bits to fit the mkII taillights and the reverse light. Then sort out the wiring and make brackets for a set of LR8s. (These would be the primary goals.)
On the interior, clean and fit some original carpets, the radio and speaker, the heater and the GTS clocks.
If it isn't going to be too expensive, it would be nice to rebuild the GTS gearbox, get it fitted and repaint the front subframe and engine bay while the engine is out. (Probably won't get to this in the year).