merging two equivalent branches

[David Reitter <david.reitter@gmail.com>]

Hello,

I have a problem with my git project, resulting from an upstream branch beyond my control being rewritten.

Can I specify parents for a revision whose history is hidden from git-log?

Concretely, I need to merge two branches that represent different conversions of the same original CVS branch (with >100k revisions).  
I've been working with converted branch B, but now we have a new branch A.  Revisions A150 and B145 correspond to the same tree, but there is no common ancestor:

A1 -> A2 -> A3 -> .. -> A150 (A)
B1 -> B2 -> B3 -> .. -> B145 (B)

I have a published downstream branch C with my own changes that started somewhere from B and has occasionally merged new developments from B.  I'd now like to switch it to A.     Future development will show up on A and I'd like to be able to merge it into C when that happens.

Using "git-merge -s ours" does this job nicely so that I can pull further development from the remote branch into mine.

However, git-log follows both parents of the new merge commit and thus shows many redundant commits.  This is OK from the logical perspective, but because I have used the "ours" merge strategy, we're guaranteed to have only one revisions in the final tree.  Thus, I wouldn't want to see all these revisions in the resulting branch.  Grafts/rewrites or git-replace would probably lead to the same issue, I reckon.

Thanks for your help.