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See if they are checking for a C-K truck or an R-V truck, a lot of parts books will list them seperatly with different engines
Pressure and return hoses for the brakes? Do you mean for the hydro boost? Like Jay2d2 said make sure they're looking up an R for 2wd or V for 4wd.
I found what you need here: www.rockauto.comThe lines you are looking for would be under the steering category. While navigating their catalog don't use the back button.Your search should go like this:Chevrolet > 1988 > R30 (I guessed at this, but fill in your application) > 6.2L 379cid V8 Diesel MFI (J) > Steering > Power steering pressure hoseFor the return lines just change the last selection to "Power steering return hose." But you should definetly be able to find this at your local auto parts store.