whats the difference between the (x and W) in the engine code vin #

Here's the deal. I have a 1997 Sonoma. I want to put a blazer fuel tank in it. The reason is its shorter, uses all gm parts, and it should fit under the rear section of the frame. behind the axle. The engine code on my vin is (x). Most blazers are code (w). Will it matter what year or engine code the blazer has when finding a fuel tank and sending unit. I figured the fuel pressure should be the same. Thanks for the help.