Just to complete this thread. I finished the plumbing project today, tying the new pex with the original, thanks to a timely delivery of new connections from jviss.
I found it easier working with the pex because I didn't spend as much time hunting in the bilge for dropped o-rings. But I am clumsier than most.
While my work does not match that of many on this site, I do like how the pex is neatly installed along the engine compartment walls rather than hanging over the engine on the way to the water heater as in the original installation.
Thanks, all.