Nice tip on the Viton O rings. I plan to pull my injector holders to get them powder coated along with the now rather rusty looking retaining rings so I will be needing new base O rings.

One thing to consider, heat soak / vapor lock is usually less of an issue on fuel injected engines because the fuel rail stays under pressure when parked which discourages boiling of the gasoline and the ensuing vapor issue. Even if you do get vapor, it should clear fairly quickly because the pump is at the back where it is cooler and is usually effective at purging the fuel system when it pressurizes.

If your fuel rail is losing pressure when parked this will increase the risk of gasoline vaporizing in the fuel rail which then complicates starting. Loss of pressure can be due to the pump discharge check valve leaking or the injectors or cold start injector leaking. If the injector or cold start injector are leaking, this will certainly complicate the hot restart problem. Watching fuel rail pressure following engine shut down will give you some idea as to whether loss of fuel pressure is contributing to your hot restart issue.

The phenolic washers won't hurt.