I actually agree with the whole just put it together and go...see what happens. I'd rather see the extra parts in the system before it is filled and bled though... taking it apart again it is messy and bleeding the system can be challenging at times. I looked up the rear hold off valve and found that it came on "all 67-70 cars with the Kelsy Hayes 4 wheel disc brake option and high performance engines". I converted a 69 roadrunner front wheel discs, using a disc drum master without a purportioning valve and it worked great. This time around I"ll be adding one as I cut the rear break line while relacing the front frame rail. I have one and figure it to be an easy way to splice the line and have it if I need it.