Maybe I'm missing something.... but I wonder if it's be easier to take the drivedrain and front end from the '84 and put into the '87.
The tunnel part of the bodies are the same, only different really is the floor pan behind it wher ethe holes for the shifters are. Oh and like you said the firewall for the clutch pedal, too.

With 200+ Billion electrical parts, the world most complicated machine is inside your own skull.

Question Reality.
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'89 Rnr DLX "SR4.5", 32s w/ 5.29 locked f/r blah blah