I reckon that would be due to your injectors, Adrian. Injector quality changes everything in how it idles and low speed/low RPM stuff. For example, SARD 800's feel like they came from the Jurassic era compared to a set of ID 2000's.
Engine number?
It's a $28 blue slip or whatever they cost now. I had to do it when I changed over to my RRR block, that was 5 years ago.
Done and dusted.