Personally I'm surprised that you find this difficult to understand, but although I will not presume to speak for Dave, I hope I may set down my thoughts again. Paul's claims may indeed be spurious: it is not part of this argument that Paul is trustworthy. But he claims to encounter a community of people in Jerusalem, and these are led by individuals who have the same names as kinsmen and associates of Jesus mentioned to in the Gospels. If Paul's "Lord" is the same as the Jesus who has such associates in the Gospels, then Paul's Lord is the Gospel Lord Jesus. That is, if such a Jesus existed, then he and he alone is the Jesus who may be defined as the HJ. But he may not have existed, if Paul's and the Gospels' accounts of this Jesus are fictitious. If they are fictitious (and they may well be) then there is NO "Historical Jesus" .
No. I do not think the above is actually correct. Look at the highlighted part - you say Paul’s Lord is the Gospel Jesus, and he alone is the Jesus who may be defined as the HJ .... well that is surely a mistake! ...
... there is no need that the Jesus described by Paul and the Gospel writers is accurately or actually the HJ ...
... a HJ of some type may have existed, but might well be very far removed from anything written in Paul’s Letters or the Gospels.
That HJ may still have served as the basis of later writing in Paul and the Gospels, but whatever is said in that writing may easily be entirely fictional. And afaik, the likely evidence suggests that it probably is fictional.
Suppose for example the accounts of Paul (and then later the Gospel authors) were actually based on someone like the Dead Sea Scrolls Teacher of Righteousness who may have lived circa. 100 BC (or even, several centuries BC). In that case there would have been a real HJ (the Teacher of Righteousness), but he would not be the Jesus figure described by Paul or any of the Gospel writers.
. No, he is defined by an association claimed (perhaps falsely!) both by the Gospels and by Paul. His existence is probable only in proportion to the credit due to the Pauline and Gospel accounts referred to above.
No. See the above.