Understood. It just depends on how much power you want to get out of it. If your staying NA, then a 6.0 or 6.2 is a better starting point. The 5.3 converts to around 325cu. If you are going to add a turbo, then it doesn't really matter, the 5.3l is a good base but then the 4L60E isn't going to hold up to that much HP.
If you go 6.0l, the LQ9 has the flat top pistons and a little higher compression. The LQ4 is dished, lower compression, better for boost. If you want even more compression on the LQ9, swap on a set of 243 or 799 heads and you'd be close to 11:1.
Most wiring harness places don't even want to touch old harnesses any longer. They take longer to tear apart than building a new one from scratch. I think I paid around $500 for a new harness and ECU from PSI Conversions.
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