In principle, I agree with Retro. If the pump is a gear pump, the check valve may not be needed.

Is it possible to move the line into the transmission from the rear plate to the top over the gears? From what I know, there is a small opening between the chamber that held the deferential that was removed and the gears. This way create a situation where that chamber would fill up, pressure then would go up to the point that the oil flow through the opening was the same as the pump. If you drill the opening larger than the fitting into the rear plate, then this would not happen, but then you would need to consider the metal shavings.