98 chevy 4x4 tahoe to gen IV 5.3 ls

ok so i bought a 2013 chevy silverado 5.3 and wanting to swap into my 98 tahoe 4x4 it is dbw 58x wheel i'm wanting to know about best place to buy a stand alone harness i also will be using my original trans 4l60e i have the harness and ecm but i dont have a tcm i can buy one from oreillyauto but wanted to know if i needed it to control the original trans or if the ecm alone would be able to its a e38 ive seen on psi conversions they have a e38 ecm and has the option to be programed for the older 13pin 4l60e but there harness only has 15-17pin trans connectors this will be my first swap so im new and a little confused and worried about it all i have dirty dingo mounts and bought the speedway motors flywheel but i might still need a spacer ive seen back and forth about needing and not