I'm not sure about the failed astartes story. I don't think it likely that a space marine chapter just lets a potential neophyte walk away with a valuable implant. I was also under the impression that the implantation process was something you either survive or you don't.
Everything else looks fine, but I think this part would be better if you took out the heart implant part and wrote it that Saul did not make it past the astartes screening process.
Nonsense is our Salvation