A picture would help, but more than likely a vacuum port not being used.I would not hook a heater hose to it .
67 coupe White/Parchment
289 .060 over T-5 and 3:80 Gears
RV style MTF-1 Cam with roller tip rockers
Edelbrock F4B with 600 DP
Tri Y with 2 1/4" H pipe Flowmaster 40s
261 RWHP 265 Ft pds TQ at 4400 RPM
Not a track car but nice from stop light to stop light!