First of all you're going to need an adapter bracket to hang the 605 on the 55. The you gotta cut the bottom half of the old 55 box off, and install it below the 605. Then you take the pitman arm shaft (think they call it a sector shaft), and grind the two outer teeth off, and drop it in the 605 box. Very difficul to explain, but if you look at the two boxes apart, it ain't so confusing. I'd contact Classic Chevy Club International, in Apopka, Fla. The sell all the hardware, and can provide you with a reprint of the tech article to show you how its done. Not a very dificult job that can be done with basic hand tools, and makes your shoebox a pleasure to drive. You won't be sorry you did it.