x2 on a LOT more info of your vehicle required .
88-up new body trucks went inboard of frame and the frame bows out the further back it goes after the cab so there not a easy fit at all .
if square body 73-87 then just get a 1987 tank for short or long bed for factory tbi injection . then a tbi sender unit minus pump . then a acdelco ep381 pump from a 1996 c3500 5.7L is a direct swap and has the psi and flow to get you started on the efi swap . or ask the place your getting efi from what pump they recommend to plug-n-play on the gm sender .
make sure you read and search a lot on efi there is good kits and bad kits . look real hard at the options and price points . learn from others troubles and try not to have the same happen to you . see my sig line below .