William Duffield, on the Cohansey
I figured out answers to two of my concerns.

No, a flat top bedrock (at least the L-N version) is not designed to fit the Stanley #52 shooting board. The chute track is 2-1/8" wide, according to Lee-Valley documentation, while the side of a L-N #7 is 1-7/8" high.

As I suspected, I do have a way to answer my question about replacement blade compatibilities. I remembered that I have a Veritas A2 blade and improved chip breaker stuffed in a tool chest that I purchased to restore a Type 13 Stanley Bailey #6 (that I still need another roundtuit to complete). I opened it up, put it together and dropped it into my L-N #7. Other than a gaping mouth opening (a trivial adjustment on any Bedrock), it works just fine. At least, my depth adjuster engages this blade and chip breaker without a problem.