Have you driven this truck before as it is? I know it's a surprise to hear but before S-10 frames existed, before Chevy trucks were even sold with IRS, when Corvettes didn't even have disc brakes these trucks were towing boats!
They towed them all over the country, I am one of them driving my dad's F100 towing a boat hundreds of miles up into the Sierras to camp. All with drum brakes and an I beam, OH THE HORRORS!
I went through the brakes in my Rambler in no time, a few days, all new lines and hoses, wheel cyl and master drums turned all done. And I drive it every single day.
The frame swap is a huge project that will have it down for a long time, often people get overwhelmed and a project like that never gets done.
My truck is going to have IRS though vintage IRS from a 49-54 passenger car (that is what fits the theme of the truck so that is what I am using) so I am not against up grading at all. I just like it to be NEEDED, people are so crazy convinced that a car HAS TO HAVE disc brakes (nope) or IRS (nope) to drive it on "modern roads" (I want to puke when I hear that term) its YOU who drives your truck and YOU can drive it stone stock every day if you want, as I do.
I just hate to see how often people think these things MUST be done, when it's not. How often will you be towing a boat? Is it on flat lands, or is it over the mountains? Really windy roads? Are you going to drive it regularly down big highways where the traffic is going 70? There are lots of questions that need to answered more than just driving on your typical city streets and all that "most" of us use our cars and trucks for. If you are commuting 60 miles a day to work, nope that's not for you, modernize it. If you are towing a boat, a motor boat, over mountains through windy roads, disc brakes at the very least are for you. One of the biggest misconceptions is how disc brakes work over drums, drums will stop the car very close to as good (my Rambler blows me away at how well it stops!) the big difference is how they work after a number of hard stops or braking like on a windy mountain road down hill, they FADE BIG TIME! That is where you wish you had discs, holy crap can they fade. But my daily driver this isn't problem not in the least, would it be with you?
Think about it, I don't know about that $600 to make your brakes work, I don't see anywhere near that much but I have a great source right on my way to work for parts. I can stop there and buy the master cyl for my Rambler and they have it in stock, did the same for my son's 63 Falcon when we put discs on that, the 68 Mustang master was right there in stock, the 78 Granada calipers were right there in stock, the tie rod ends, everthing was right there in stock and reasonably priced, we all don't have it this good. The brake lines, OMG it's so easy to change them it's funny. These days in a good parts store they have a row of lines, all different lengths from a few inches to three feet. On my son's Falcon and my Rambler I only really had to cut one line and flare it at one end, done deal. The rest of them were all right off the rack at the parts store. They have a new tubing that has sort of a black look, they bend real easy and you don't even need a tubing bender to do it.
http://www.oreillyauto.com/site/c/se...0833/C0066.oap Outside of wrapping it around a pipe or something for a nice tight bend you don't even need a tool! You need a 5' long line you put a 3' and a 2' simple fitting to tie them together, it's so easy it's crazy.
All I suggest is you think about it, do you REALLY need the IRS and Discs or just the discs maybe?
Brian