I'm converting a 6x6 to diesel and hoping to run hydroboost brakes. All the hydroboost information on the net seems to be about 4-wheelers. Does anyone know whether any of the commonly available hydroboost units have enough capacity to handle a 20000 lb truck with six, inch-and-a-quarter wheel cylinders? I don't plan to convert to disc brakes, just get the original drum brakes to work.  

hydroboost should accommodate vehicles up to 25,999 GVWR. though i haven't seen any on a 6x6 before. the best thing you could do is maybe go to like a international dealer and look at their trucks that have hydraulic brakes and see what kind of setup they have and do a little research  

Go to a truck wrecking yard and look for: 80's & 90's F600-800, or GMC/Chevy 45-6500, see if you can find one with tandem rears. Then you can snag all the Hydroboost goodies.  

As mentioned, go look for a GM or Ford tandem truck.  In my area, the GM's are more common.  They were not a true live tandem, but the rear axle was a tag that was run by a belt drive system.  Yes, belt drive.

Wait.... this 6x6 doesn't have a hydro boost right now???  How old is the thing?  It's not an old 6x6 w/ the GMC 302 engine is it?  I thought those were all power brakes (aka hydroboost).....  The wheel cylinders are 6 1/4 in diameter or long???  That seems big to me....but I'm use to seeing trucks w/ duel wheel cylinders per wheel vs just one.....