Line Lock - front or rear??

Line locks can most certainly be installed to block pressure from the rear brakes, in the rear brake line, making burnouts easier to control (in some folks' opinion) by using your foot to control front brake pressure as opposed to having them controlled by an on/off switch. I've done it both ways on a couple cars and either way works fine.

I just checked the 2020 NHRA rules, and it appears that NHRA prohibits plumbing line-locks in rear brake lines in some pro classes, but is not specified in the general requirements. All it says is that "All line-locs (electric or hydraulic) must be self-returning to normal brake operating mode" - meaning momentary switch is required, I'm assuming. I've noticed quite a few guys at the track run them on the rear lines.