Basically if I just screwed this on as is, I can imagine the flange
sitting up off the hull
about 1/2". Is this the wrong piece of hardware for what I have in
place already?
No, I think it's the right one. Have you shopped around the
on-line discount retailers? It's possible you could save some.
I took a quick look and found a different kind that is
substantially cheaper.
The place where they saved money making this one is obvious,
the valve body is much smaller & the handle cheaper
(although I dunno if the Groco handle is really any better).