^^ This. When I was researching my swap, TONNES of people tried to convince me to go carb, citing simplicity, but with no regard to fuel economy. I did not find the swap very difficult at all, and it was my first engine swap.
The XJ pump will provide sufficient volume (debatable), but will not provide sufficient pressure to power an MPFI 5.3L. I believe the XJ's FP is around 40psi, while the 5.3 wants 60psi. Running 40psi to the 5.3 results in poor fuel economy as well as a lean condition at higher RPM.
Wow... the TBI I'm using for my 350 only needs 43 psi. The (replacement) stock oem-style pump was pushing 50 psi when I first dropped it in, I had to tune it down at the regulator.
I'm only pushing the oe-style fuel pump because in-tank is hands down the best way to do a fuel pump, and oe-style is the easiest way to achieve this. You don't have to put in a new fuel tank since it was already set up for injection.. the inline, out-of-tank solutions all need to be mounted below the lowest point of the fuel tank, which is great for a corvette or a street rod, but horrible for our application.
Just pointing this out as something to think about-- I literally just went through this. Beautiful build btw.
I FINALLY got my tbi running today.. really, I found it far, far easier to swap in and tune than a carb. I really never should have let myself be convinced to go with a carb in the first place (especially given that the hard part -- the supply and return line -- are already in place.. something I had to completely redo).
Keep the pics coming!