Even for those who have JB6 brakes on their truck, if the calipers aren't original you have to ask yourself "Do I
really have Low-drag calipers on my truck?" (as noted in the attached Bendix / Allied Signal document), and, if you really do, "Are they working as intended?", which may not be the case. Finally, ask "If I buy JB6 replacements, will
they actually be 'Low-drag' calipers?" (see attached document).
These are a few reasons why I simply replaced the JB6 front brakes on my Suburban and installed components (NBS / JB7) which were not, by design, "Quick take up / Low drag".
However, the NBS MC has a larger bore than another alternative MC, which is the GMT400 8600# MC. Both MCs are non "Quick take up". Using the latter would mitigate the loss of hydraulic advantage that
@Schurkey mentioned above.