I wouldn't read a lot into the "Hint" it hasn't been signed off.
"Tada says in broken English"
"but he
hinted that Toyota has yet to sign off on an 86 Mark II."
It would appear they at least talked to him (appearances can be deceiving though) which makes this statement the most interesting of all:
"Tada-san
bristles at the suggestion of adding a turbocharger – say, for example, the
Subaru WRX’s 268-hp boxer engine, which would negatively affect the linearity of the power band."