Someone jump in and tell me how wrong my memory is. But here goes...
On our cars, doesn't the proportioning valve send only one line to the ABS block for the front wheels, and it gets broken out at that point for each individual wheel. As I understand it, a typical line lock installation has the solonoid down by the ABS block, on the input line. If that line is the same line coming out of the front/rear proportioning valve up by the master cylinder, then I would think it would be fine to install the line lock up there as long as you can find a place for it. Should still lock both front wheels as planned, and the wiring should be a little easier 'cause it would be a straight shot to the firewall.
Or maybe my memory is wrong. Joe Lynch has a nice writeup somewhere, I'll go search for it. It's for his 99 Cobra, but ours is pretty similar as I understand it.
Dave