Not to thread jack but I'm interested in this myself. I've read that 862 ported and milled will do wonders on the 4.8/5.3. 243 would have to be milled from my understanding just to get back to factory type compression. I could be very wrong but I'm going to have a set of 862 worked and see because they are usually cheaper. Hopefully someone with more knowledge and experience will chime in.