TH400 vacuum hookup question

[**grumpy**]

My 66 burb has a 250 inline 6. The PO put a new TH400 behind it when the 3spd manual gave up the ghost.
Thing is he never hooked up vacuum modulator. It runs great but it runs out forever and taxes the motor before each shift.
Being it had a 3spd, there isn't a plugged vaccum port anyway to use, so what's best place to T off to use for the modulator?
I hate winding motor out on every shift. Plus harder on gas.
Thanks
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[aerotruk63]

There should be a plug on the intake below the carb on the drivers side of course. There were manifolds available to plum it all together. They had fittings for the assisted brakes, Vacuum gauge etc.

[**grumpy**]

Yep. There is a plug in the manifold, just as you said. I was thinking that was the likely spot to use.
Project for tomorrow.
Thanks
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