It's not actually your lower injector seals causing the problem unless they're hard as nails. It's really a tolerance issue. The fuel rail is held on with spacers to compensate for the thick portion of the body of the injectors. The upper seals work like a spring to press the injectors into the lower seals off of the bottom of the fuel rail. You can replace lower seals and still leak afterwards like I did if the upper seals are bad. I'm not talking about the o-rings that seat into the fuel rail. I'm referring to the rubber ones that fit down over the whole upper shaft on the injector.
There are various ways of modifying the upper seals to make the injectors press harder into the lower seals... but I found that a $4.99 assorted box of grommets from Harbor Freight
has a set of 5/16" grommets in it that are a hair thicker and slightly less-pliable than the factory upper seals, but not thick enough to push the upper seal out of the rail. They work beautifully and I've boosted it to 40 PSI on the same leaky lower seals while boost leak testing, and not a single leak. They also cost 1/4 as much and you're left with 96 spare grommets for your next 50 wiring jobs.
Have that little nugget.
EDIT: OH... hey... yeah that bit about your fuel pressure regulator... Is it leaking gas into your intake manifold? Pull the vacuum line after it's been running and see if fuel dumps out. That could be really bad.