I just came across this old thread while searching for a few items...
I went ahead and installed a hydro unit so here are my thoughts:
I purchased a complete (new) ACDelco system that would have fit a '99 3/4t Suburban w/rear drums. Here's a link to all the part #'s http://www.gmc4x4.com/topic/120-hydroboost-conversion-part-s/?hl=hydroboost
For this to work properly and not overheat, you really need to purchase everything in the part list (then there's no need for a "t" connector). Also, you have to remove the variable speed sensor for the system to function properly and install the GM bypass.
Also, the hydro brake pedal were notoriously difficult to find, but LMC now sells them brand new for $35 IIRC.
One important aspect to pay attention to -- different hydro units and PS pumps have different pressure ratings...so try not to mix & match. Find one truck you want to mock your system off of and stick with that setup.
I hope this helps!!
Can you comment on how your steering is w/o the variable speed assist? I read another poster complain that it made his already not tight steering very--forgetting his words--floaty(?). Comments on steering after the bypass? THX!