The 243's are the best STOCK cathedral port head, and by far not even remotely close to whats available out there today as far as performance. A set of CNC ported 243's are worth upwards of 30-40whp. TSP makes a great 5.3 head that would work great on the LS4's for very cheap fully assembled.
I'm surprised you guys don't visit the LS4 forum more often on ls1tech lol you guys are aware that you can run any LS cam in these cars once you do away with the DoD which is as simple as installing regular LS lifters and trays and a LS3 valley cover. Here's mine with a 214/220 cam. Furches im sure uses a slightly different spec for the turbo builds where as mine is built to run NA.
https://www.youtube.com/watch?v=SQRdQr7tDKA