I'm coming late to this party but I just did this on my 1973 Suburban. This will work on any 73-91 burb or 73-87 squarebody Chev.
I was surprised how simple this conversion was.
Here is a summary of what I did, using a 1983 K30 as a donor (craigslist) however you can get all these parts "new" from rockauto for under $400.
Hydroboost
1983 K30 unit is a direct bolt in to the fire wall.
Pedal linage works ok, though the eye is a different size (HB is larger). No mods at all required. ( read somewhere that one is 1/2 and one is 9/16 )
Power steering Lines
*1983 K30 stock lines that came with the donor. No mods.
Pump Bracket
This one was tricky because I assumed they would all work.
Options were: 1973 original, 1983 K30 (broken), 1984 K20 (not the same!)
I tried the 84 but the pump would not mount up.
Pump Bracket: 1973 K10 original bracket
Notes:
Pump
1983 K30 from the donor.
Notes: This one has two return lines (from gearbox and from hydroboost); USE THIS, I have read that using a "T" for the return lines will give you issues.
Pulley:
Single pulley from the stock 73 K10
Gearbox
1984 Saginaw gear box.
I had this laying around and used it because all the lines are metric and bolt right in.
Notes: 73 K10 uses a different size input shaft (larger)
Mods required: The input shaft is a different size on my 73 K10 vs the 84 K20.
I bought a new rag joint that has the correct size. This was horrendously expensive! $46
My write up is here:
http://67-72chevytrucks.com/vboard/showthread.php?t=701079
After driving it some, here are conclusions.
Pedal feel is very firm and "wooden". Some don't like that. The vacuum brake set up is more ... sensitive feeling. Hydroboost is like stepping on a 2x4, and you stop. Not delicate feeling.
This fixed my braking issues, which I believe are the result of low vacuum produced by my worn out 350. So I'm happy with that.