Wilwoods all around and residual line pressure...

Well folks, I just finished putting Wilwoods on all fours in my '67 Barracuda. I think I may have made a mistake by leaving the original master cylinder in place (dual reservoir).

The problem I'm having is excessive drag on the brakes now. I was told that there's a check valve in the MC that keeps pressure in the lines and that I should either remove it or get the proper MC.

Any suggestions?