the 203 k20 trucks were commonly like that with two sizes of U joints, you usually wont find one with same u joints on both ends, i have had quite a few 73-80 k20 203 trucks and they have all been this way including this 79 out here right now, thats just how they are, and also most all of them run 56" light rear springs setup but with HD 3 leaf front packs and sway bar heavy front setup, very wierd odd combo but it is what GM did in the 70s on this particular model,
good luck