Hi Gaz
I have also seen that warning, and seen it de-bunked on here a couple of times - I guess the Supra ABS unit is forgiving.
In an ideal world we'd be able to tap the brake lines *after* the ABS actuator, but that would involve switching two separate brake lines, left hand side and right hand side - but the hurst model only has one solenoid.
I plan to tap into the brake line at the master cylinder, underneath where you fill the brake fluid. The line at the back of the engine towards the firewall is the one for the front brakes (Don't take my word for it, I still need to confirm this).
This will be blocking before the ABS unit, so in theory the ABS ECU could sense the brakes not releasing, and cause problems.
Of course, pulling the ABS fuse would stop it from interfering in the worst case but I'd quite like to hear from knowledgeable sources on here.