It depends on the year and model of your truck and the current tap installed. Most likely there is a chunk of cast aluminum with fittings cut into your fuel filler hose already. Put on your scrubbies, crawl under with a flashlight, and take a look at what you already have.
It should look similar to these nice ones Mr. Cobb sells
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If you are really lucky there may be a provision for a return line already there that is capped.
Or maybe there will be a place with enough beef in the casting where you could pull it out and drill and tap for a fitting, if you are handy at such things.
Assuming the new slide in is fuel injected, and your current slide in has carburetor, you will need to upgrade your fuel pump for the unit as well. Carbs need 4 to 7 psi to operate and fuel injection systems run at 30 to 60 psi. Your existing fuel pump to machine fuel line may need upgraded too.
IMHO - whatever you do - do it right, your fuel system is not something to be trifled with.