My 78 and for that matter the 87, only had centre face and screen working,
Mostly due to the fact that the stuff was ripped out and trashed - esp in the 87.
I looked at what was missing (ie. Pics, US parts cats, 78 build book etc). Then did the rounds of the junk yards.
Once you have the missing bit in your minds eye, its not too hard to imagine a holden/ford/nissan or what ever part doing the job.
Plus some epoxy and glass mat, one bit is even a "coreflute" type material, cut and pasted, painted black. (Coreflute= house 4 sale sign).
The 87 has the right side face vent connected via a white corregated section of home A/C piping cover tube.
The joins just need either Clarke rubber foam or Bunnings foam draft excluder strips with the seft adhesive backing, which is basically whats in the cars from new. Just remember any tape you use, with a locked car in Aussie heat, means crappy sticky gunky crud. Never use the dreaded black electricians tape - an absolute no no.
Better use the Aluminium duct tape, it handles hot and cold better, and because it is hardish, it can be moulded to shape. Good luck with it.