[blucar]

When I was much younger I street raced my '36 w/46-48 Columbia w/3.78 gearing, that has a well built 59AB engine.
I modified the electric over vacuum shift system with a toggle switch that controlled the power to the solenoids. Controlling the power to the solenoids cut the power to the clutch switch which prevented the down shift when the clutch was depressed.
I used the Columbia as a six speed, low/low-over, 2nd/2nd-over, 3rd/3rd-over like a big truck 2 speed rear end.
On many occasions while street racing I would shift the trans to 2nd gear, then the Columbia to OD which gave me a gear range higher than 2nd, but lower than high gear. the '36 would run at 100 mph plus in 2nd over so I would not have to shift into 3rd, if I did shift into 3rd I would be in 3rd OD.
I never experienced any trouble with the Columbia shifting at speeds over 40 mph, I regularly used the Columbia as a passing gear, briefly tapping the clutch as I released the throttle.
The attached pix shows the location of the solenoid valve pack mounted to the inner fender panel in lieu of the left cylinder head like the stock '46-48 setup.