Brain Freeze: Transferring Current SSD to New-to-me MBP (Mid2012)

I know how to do this, but my brain is frozen and I can't piece together the steps.

I have a Mid-2012 MBP (Boots from an SSD, has data doubler with 500GB HDD, El Capitan, 2.3GHz, NVIDIA 512MB graphics processor) --we'll call this one A -- that started having logic board problems. It boots and operates fine until something physically jiggles and *poof* kernel panic. But, it does run.

I just picked up another Mid-2012 MBP -- we'll call this B -- to replace my current one. B has its optical drive intact, is booted from a 750GB HDD, has a 2.6 GHz processor with the NVIDIA 1GB graphics card, and is running Sierra.

In the end, I want:

1) SSD Boot Disk from A --> Boot disk for B

2) Data doubler from A --> B

3) 500GB from A --> 750GB B in that data doubler.

2 & 3 I get... but it's transferring over the Bootable SSD that's making me think.

Any help?

Well... the point is somewhat moot.

Having just opened up B for the first time, what was sold as a 750GB HDD is actually a Crucial MX300 SSD.

I'm still going to swap A's Samsung EVO 850 in place of the Crucial (faster drive, no need to transfer files new Crucial), but if that doesn't work, I'll probably just take the easy road and migrate from SSD A to SSD B.

Feeling kinda lucky right about now (knocking on wood)...