Buy the Chevrolet Truck Shop Manual for the year of your engine. They are available from all vendors and are often for sale on eBay.

What year is your engine? This is important to know before purchasing a Truck Shop Manual, because in some years between 1954-1962 the Shop Manual is only a supplement to the previous year's Shop Manual (you'll want to purchase both year's manuals).

The Truck Shop Manuals for 54-62 that have 235 information also contain 261 information (all these truck USA truck engines had mechanical lifters).