Yes, Purdey bolting and Purdey double underlugs are the same thing.

"If Clipped Fences (and/or the extended rib) are desireable why don't you see them on most DR's?"

Very funny. You ARE kidding, RIGHT??? You DO see rib extensions on most (virtually all) good quality DRs. What you don't see them on is today's cheap repros. With respect to sideclips, no, they're not particularly common on any doublegun, and they're redundant on a DR with a doll's head anyway.

"Are they hard to incorporate into a DR correctly?"

Not necessarily hard, just more expensive to make as more hand fitting must be done, which is why you don't see them on the cheap stuff.
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