Gauges and the wiring harness

[TTU713]

I plan on doing a 4.3L to 5.7L LS1

What I seem to not understand about the swaps (looking through a few here) is the gauges. How does the stock cluster work if you were to order an aftermarket wiring harness? For example, I have an EFI CONNECTION wiring harness from my last v8 swap, all the harness did was control the engine/trans (it had it's own pcm, did not come with wiring for any emissions/rear o2s) which meant I was not able to use any gauges unless they were aftermarket

My guess is that I will HAVE to buy a stock 5.3L engine harness/pcm and have it flashed somewhat to work with the LS1. Which would seem to also allow the stock gauge cluster in the Silverado to work. So buying a full 5.3L harness and replacing the 4.6L harness with it, would pretty much allow me to throw the ls1 in there and plug everything up and be 100% ready to go


also, seems a lot of people on the site refer to an LS1 as the 5.7 AND 5.3L, it is somewhat confusing - but can I consider the 2 EXACTLY the same as far as major parts (like wiring/mounting)