Not familiar w electronics on 84 Chevette, but wasn't torque converter lockup electronically controlled, requested by ECM after motor warmed up and vehicle speed correct? I suspect you don't have ECM on your kit car.
That said, the tach can tell also, if you have one. When TC is locked-up, engine RPM does not change with small changes in throttle. The tach needle won't move without a vehicle speed change.
Good Luck,
Bill
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