A-518 Lockup and OD question

I think PATC sells an adjustable vacuum switch for that purpose. They also sell the hydraulic pressure switches to actuate the OD and lockup solenoids, but it sounds like you've got that covered.

Performance Automotive Transmission Center
I think this is what you are talking about...

https://transmissioncenter.net/shop...ick-here-for-727-to-46rh-swap-wiring-diagram/