Funny how times change.. No doubt in the late 1970s or 1980s, someone thought "no one wwants a crappy longhood, so I'll 'update' it to look newer.
fast forward another 10-20 years and now no one wants an impact bumper car but a longhood
The 2.7 was also a "period" upgrade. As a driver it is fine. As a "track ratt", it is fine. As a concours car, I wouldn't spend time or money.
For comparison, what is the market like for a 1974 (impact bumper) car? Based on the condition you describe, what would you pay?
iirc, the '74S was rated at 167hp sae net (175 din). The 75-77S motors were down another 10hp due to smog (157hp). Either way, a 73 T was rated at 140hp so its still a slight upgrade.
These CIS motors do not mod easily unless you crack open the motor and replace the cams. Might get 5-10hp with SS heat exhangers and a sport muffler.