Inquisitor 1538

[Ripper]

I'm seriously struggling with this one (but, as usual, I'm determined to crack it!)
Across answers must be changed by mistake. I've sorted some out by just removing one letter (always from the same position) but I'm really stuck with 7 across: Overwhelming gains with renegade having backed Prime Minister (4) I'm sure the answer is swamping but don't know how to change it! Likewise 42 across Historian yearning after upper crust (4) I think the historian is Sallust with the 'i' removed from sial (upper crust) I assume 'pick up the pieces' refers to the extra letters removed from the across answers?
Basically I need help!
Thanks in advance

[ProfessorMaisie]

Your answers are right, you just need to remove some letters to make 4 letter words for the entries.
Only the mistakes in the 7 symmetrical answers contribute to the phrase. These all have more than 1 letter wrong (so your 7ac and 42ac are parts of it) and they don't appear in clue order in the phrase - but they do remain as discrete blocks.

[Ripper]

Thank you ProfessorMaisie, how do I know what letters to remove?
I'm really having a hard time with this and I'm completely stuck!

[ProfessorMaisie]

Never lose the first or last letter, the letters that are removed are always consecutive.

[Ripper]

Thank you all