its a 4400 or bigger, for sure. the 1/2 ton front end will fit if you have one.
here is a guy building a very nice 1/2 ton on a K20.
http://67-72chevytrucks.com/vboard/s...d.php?t=726477
for what its worth, the 1/2 ton does not fit an s10 very well unless you stretch the front wheel track significantly. I put a 65 swb on an s10 and widened the control arms 4 inches per side.